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 $182.37   10.511%   $201.5389   $201.54   $201.55   $201.50  
  Purchase #2 $148.43   4.543%   $155.1732   $155.17   $155.15   $155.20  
  Purchase #3 $63.39   10.829%   $70.2545   $70.25   $70.25   $70.30  
  Purchase #4 $42.88   9.218%   $46.8327   $46.83   $46.85   $46.80  
  Purchase #5 $226.34   12.214%   $253.9852   $253.99   $254.00   $254.00  
  Purchase #6 $112.31   13.419%   $127.3809   $127.38   $127.40   $127.40  
  Purchase #7 $200.52   3.292%   $207.1211   $207.12   $207.10   $207.10  
  7 purchase totals = $976.24       $1,062.2865   $1,062.28   $1,062.30   $1,062.30