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 $230.36   10.245%   $253.9604   $253.96   $253.95   $254.00  
  Purchase #2 $204.30   4.269%   $213.0216   $213.02   $213.00   $213.00  
  Purchase #3 $167.41   6.834%   $178.8508   $178.85   $178.85   $178.90  
  Purchase #4 $41.92   7.285%   $44.9739   $44.97   $44.95   $45.00  
  Purchase #5 $187.81   6.526%   $200.0665   $200.07   $200.05   $200.10  
  Purchase #6 $236.39   4.287%   $246.524   $246.52   $246.50   $246.50  
  Purchase #7 $82.95   4.753%   $86.8926   $86.89   $86.90   $86.90  
  7 purchase totals = $1,151.14       $1,224.2898   $1,224.28   $1,224.20   $1,224.40