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 $88.79   8.717%   $96.5298   $96.53   $96.55   $96.50  
  Purchase #2 $107.65   8.421%   $116.7152   $116.72   $116.70   $116.70  
  Purchase #3 $49.96   9.339%   $54.6258   $54.63   $54.65   $54.60  
  Purchase #4 $17.35   7.125%   $18.5862   $18.59   $18.60   $18.60  
  Purchase #5 $170.69   12.743%   $192.441   $192.44   $192.45   $192.40  
  Purchase #6 $215.93   3.672%   $223.8589   $223.86   $223.85   $223.90  
  Purchase #7 $213.52   6.413%   $227.213   $227.21   $227.20   $227.20  
  7 purchase totals = $863.89       $929.9699   $929.98   $930.00   $929.90