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 $243.58   3.434%   $251.9445   $251.94   $251.95   $251.90  
  Purchase #2 $89.56   3.138%   $92.3704   $92.37   $92.35   $92.40  
  Purchase #3 $219.95   7.597%   $236.6596   $236.66   $236.65   $236.70  
  Purchase #4 $10.66   11.754%   $11.913   $11.91   $11.90   $11.90  
  Purchase #5 $23.63   5.551%   $24.9417   $24.94   $24.95   $24.90  
  Purchase #6 $213.32   6.179%   $226.501   $226.50   $226.50   $226.50  
  Purchase #7 $179.49   4.833%   $188.1648   $188.16   $188.15   $188.20  
  7 purchase totals = $980.19       $1,032.4950   $1,032.48   $1,032.45   $1,032.50