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 $164.93   12.740%   $185.9421   $185.94   $185.95   $185.90  
  Purchase #2 $22.45   9.240%   $24.5244   $24.52   $24.50   $24.50  
  Purchase #3 $120.96   7.436%   $129.9546   $129.95   $129.95   $130.00  
  Purchase #4 $228.36   8.336%   $247.3961   $247.40   $247.40   $247.40  
  Purchase #5 $46.30   9.617%   $50.7527   $50.75   $50.75   $50.80  
  Purchase #6 $139.41   6.851%   $148.961   $148.96   $148.95   $149.00  
  Purchase #7 $59.45   13.262%   $67.3343   $67.33   $67.35   $67.30  
  7 purchase totals = $781.86       $854.8652   $854.85   $854.85   $854.90