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 $218.71   11.472%   $243.8004   $243.80   $243.80   $243.80  
  Purchase #2 $5.43   11.229%   $6.0397   $6.04   $6.05   $6.00  
  Purchase #3 $103.52   8.826%   $112.6567   $112.66   $112.65   $112.70  
  Purchase #4 $210.82   9.177%   $230.167   $230.17   $230.15   $230.20  
  Purchase #5 $167.48   11.820%   $187.2761   $187.28   $187.30   $187.30  
  Purchase #6 $116.72   7.532%   $125.5114   $125.51   $125.50   $125.50  
  Purchase #7 $227.79   8.179%   $246.4209   $246.42   $246.40   $246.40  
  7 purchase totals = $1,050.47       $1,151.8722   $1,151.88   $1,151.85   $1,151.90