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 $48.27   8.156%   $52.2069   $52.21   $52.20   $52.20  
  Purchase #2 $106.68   13.819%   $121.4221   $121.42   $121.40   $121.40  
  Purchase #3 $108.50   7.488%   $116.6245   $116.62   $116.60   $116.60  
  Purchase #4 $211.65   7.855%   $228.2751   $228.28   $228.30   $228.30  
  Purchase #5 $219.36   11.229%   $243.9919   $243.99   $244.00   $244.00  
  Purchase #6 $67.68   4.731%   $70.8819   $70.88   $70.90   $70.90  
  Purchase #7 $85.57   9.214%   $93.4544   $93.45   $93.45   $93.50  
  7 purchase totals = $847.71       $926.8568   $926.85   $926.85   $926.90