Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.46   4.102%   $246.1596   $246.16   $246.15   $246.20  
  Purchase #2 $218.65   8.191%   $236.5596   $236.56   $236.55   $236.60  
  Purchase #3 $139.96   7.661%   $150.6823   $150.68   $150.70   $150.70  
  Purchase #4 $195.62   5.180%   $205.7531   $205.75   $205.75   $205.80  
  Purchase #5 $99.74   10.573%   $110.2855   $110.29   $110.30   $110.30  
  Purchase #6 $182.94   6.505%   $194.8402   $194.84   $194.85   $194.80  
  Purchase #7 $174.79   12.416%   $196.4919   $196.49   $196.50   $196.50  
  7 purchase totals = $1,248.16       $1,340.7722   $1,340.77   $1,340.80   $1,340.90