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 $138.55   9.834%   $152.175   $152.18   $152.20   $152.20  
  Purchase #2 $61.31   4.641%   $64.1554   $64.16   $64.15   $64.20  
  Purchase #3 $177.50   12.671%   $199.991   $199.99   $200.00   $200.00  
  Purchase #4 $243.29   13.655%   $276.5112   $276.51   $276.50   $276.50  
  Purchase #5 $61.29   4.462%   $64.0248   $64.02   $64.00   $64.00  
  Purchase #6 $232.73   10.737%   $257.7182   $257.72   $257.70   $257.70  
  Purchase #7 $11.66   4.735%   $12.2121   $12.21   $12.20   $12.20  
  7 purchase totals = $926.33       $1,026.7877   $1,026.79   $1,026.75   $1,026.80