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 $233.41   8.339%   $252.8741   $252.87   $252.85   $252.90  
  Purchase #2 $119.55   5.355%   $125.9519   $125.95   $125.95   $126.00  
  Purchase #3 $90.58   7.375%   $97.2603   $97.26   $97.25   $97.30  
  Purchase #4 $99.87   4.764%   $104.6278   $104.63   $104.65   $104.60  
  Purchase #5 $96.30   9.445%   $105.3955   $105.40   $105.40   $105.40  
  Purchase #6 $138.62   5.322%   $145.9974   $146.00   $146.00   $146.00  
  Purchase #7 $183.25   6.255%   $194.7123   $194.71   $194.70   $194.70  
  7 purchase totals = $961.58       $1,026.8193   $1,026.82   $1,026.80   $1,026.90