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 $64.78   6.398%   $68.9246   $68.92   $68.90   $68.90  
  Purchase #2 $223.46   10.561%   $247.0596   $247.06   $247.05   $247.10  
  Purchase #3 $133.58   6.697%   $142.5259   $142.53   $142.55   $142.50  
  Purchase #4 $68.97   8.865%   $75.0842   $75.08   $75.10   $75.10  
  Purchase #5 $222.38   11.604%   $248.185   $248.19   $248.20   $248.20  
  Purchase #6 $156.62   3.126%   $161.5159   $161.52   $161.50   $161.50  
  Purchase #7 $84.51   9.645%   $92.661   $92.66   $92.65   $92.70  
  7 purchase totals = $954.30       $1,035.9562   $1,035.96   $1,035.95   $1,036.00