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 $165.99   11.347%   $184.8249   $184.82   $184.80   $184.80  
  Purchase #2 $217.38   13.773%   $247.3197   $247.32   $247.30   $247.30  
  Purchase #3 $51.30   8.731%   $55.779   $55.78   $55.80   $55.80  
  Purchase #4 $220.96   3.338%   $228.3356   $228.34   $228.35   $228.30  
  Purchase #5 $45.31   13.292%   $51.3326   $51.33   $51.35   $51.30  
  Purchase #6 $122.81   8.183%   $132.8595   $132.86   $132.85   $132.90  
  Purchase #7 $92.49   9.761%   $101.5179   $101.52   $101.50   $101.50  
  7 purchase totals = $916.24       $1,001.9692   $1,001.97   $1,001.95   $1,001.90