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 $146.49   11.364%   $163.1371   $163.14   $163.15   $163.10  
  Purchase #2 $187.97   12.721%   $211.8817   $211.88   $211.90   $211.90  
  Purchase #3 $193.85   3.660%   $200.9449   $200.94   $200.95   $200.90  
  Purchase #4 $14.85   9.837%   $16.3108   $16.31   $16.30   $16.30  
  Purchase #5 $116.68   10.786%   $129.2651   $129.27   $129.25   $129.30  
  Purchase #6 $39.65   7.228%   $42.5159   $42.52   $42.50   $42.50  
  Purchase #7 $243.99   7.445%   $262.1551   $262.16   $262.15   $262.20  
  7 purchase totals = $943.48       $1,026.2106   $1,026.22   $1,026.20   $1,026.20