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 $161.95   8.640%   $175.9425   $175.94   $175.95   $175.90  
  Purchase #2 $68.49   10.690%   $75.8116   $75.81   $75.80   $75.80  
  Purchase #3 $18.49   8.146%   $19.9962   $20.00   $20.00   $20.00  
  Purchase #4 $204.82   10.489%   $226.3036   $226.30   $226.30   $226.30  
  Purchase #5 $152.81   12.666%   $172.1649   $172.16   $172.15   $172.20  
  Purchase #6 $116.43   5.873%   $123.2679   $123.27   $123.25   $123.30  
  Purchase #7 $60.55   11.171%   $67.314   $67.31   $67.30   $67.30  
  7 purchase totals = $783.54       $860.8007   $860.79   $860.75   $860.80