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 $83.97   12.826%   $94.74   $94.74   $94.75   $94.70  
  Purchase #2 $137.65   4.471%   $143.8043   $143.80   $143.80   $143.80  
  Purchase #3 $200.29   11.598%   $223.5196   $223.52   $223.50   $223.50  
  Purchase #4 $86.66   6.156%   $91.9948   $91.99   $92.00   $92.00  
  Purchase #5 $76.94   10.623%   $85.1133   $85.11   $85.10   $85.10  
  Purchase #6 $229.52   6.770%   $245.0585   $245.06   $245.05   $245.10  
  Purchase #7 $69.57   6.507%   $74.0969   $74.10   $74.10   $74.10  
  7 purchase totals = $884.60       $958.3274   $958.32   $958.30   $958.30