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 $245.94   12.310%   $276.2152   $276.22   $276.20   $276.20  
  Purchase #2 $136.58   9.624%   $149.7245   $149.72   $149.70   $149.70  
  Purchase #3 $165.47   13.270%   $187.4279   $187.43   $187.45   $187.40  
  Purchase #4 $186.74   12.387%   $209.8715   $209.87   $209.85   $209.90  
  Purchase #5 $218.79   4.566%   $228.78   $228.78   $228.80   $228.80  
  Purchase #6 $166.83   3.868%   $173.283   $173.28   $173.30   $173.30  
  Purchase #7 $195.52   7.367%   $209.924   $209.92   $209.90   $209.90  
  7 purchase totals = $1,315.87       $1,435.2261   $1,435.22   $1,435.20   $1,435.20