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 $61.80   12.213%   $69.3476   $69.35   $69.35   $69.30  
  Purchase #2 $219.90   10.630%   $243.2754   $243.28   $243.30   $243.30  
  Purchase #3 $107.40   13.292%   $121.6756   $121.68   $121.70   $121.70  
  Purchase #4 $112.77   3.570%   $116.7959   $116.80   $116.80   $116.80  
  Purchase #5 $11.75   13.728%   $13.363   $13.36   $13.35   $13.40  
  Purchase #6 $239.86   5.850%   $253.8918   $253.89   $253.90   $253.90  
  Purchase #7 $52.64   11.654%   $58.7747   $58.77   $58.75   $58.80  
  7 purchase totals = $806.12       $877.1240   $877.13   $877.15   $877.20