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 $52.76   13.692%   $59.9839   $59.98   $60.00   $60.00  
  Purchase #2 $32.25   6.684%   $34.4056   $34.41   $34.40   $34.40  
  Purchase #3 $109.88   10.394%   $121.3009   $121.30   $121.30   $121.30  
  Purchase #4 $202.90   8.326%   $219.7935   $219.79   $219.80   $219.80  
  Purchase #5 $141.52   9.756%   $155.3267   $155.33   $155.35   $155.30  
  Purchase #6 $135.41   13.814%   $154.1155   $154.12   $154.10   $154.10  
  Purchase #7 $57.35   5.755%   $60.6505   $60.65   $60.65   $60.70  
  7 purchase totals = $732.07       $805.5766   $805.58   $805.60   $805.60