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 $203.83   6.208%   $216.4838   $216.48   $216.50   $216.50  
  Purchase #2 $208.28   13.412%   $236.2145   $236.21   $236.20   $236.20  
  Purchase #3 $67.92   7.658%   $73.1213   $73.12   $73.10   $73.10  
  Purchase #4 $186.79   11.219%   $207.746   $207.75   $207.75   $207.70  
  Purchase #5 $55.86   6.270%   $59.3624   $59.36   $59.35   $59.40  
  Purchase #6 $159.77   5.820%   $169.0686   $169.07   $169.05   $169.10  
  Purchase #7 $70.65   4.128%   $73.5664   $73.57   $73.55   $73.60  
  7 purchase totals = $953.10       $1,035.5630   $1,035.56   $1,035.50   $1,035.60