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 $238.49   11.414%   $265.7112   $265.71   $265.70   $265.70  
  Purchase #2 $229.72   9.352%   $251.2034   $251.20   $251.20   $251.20  
  Purchase #3 $85.32   13.646%   $96.9628   $96.96   $96.95   $97.00  
  Purchase #4 $6.69   5.268%   $7.0424   $7.04   $7.05   $7.00  
  Purchase #5 $127.62   12.349%   $143.3798   $143.38   $143.40   $143.40  
  Purchase #6 $88.49   3.867%   $91.9119   $91.91   $91.90   $91.90  
  Purchase #7 $141.51   9.850%   $155.4487   $155.45   $155.45   $155.40  
  7 purchase totals = $917.84       $1,011.6602   $1,011.65   $1,011.65   $1,011.60