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 $58.64   13.457%   $66.5312   $66.53   $66.55   $66.50  
  Purchase #2 $18.55   9.427%   $20.2987   $20.30   $20.30   $20.30  
  Purchase #3 $69.68   6.364%   $74.1144   $74.11   $74.10   $74.10  
  Purchase #4 $159.57   3.661%   $165.4119   $165.41   $165.40   $165.40  
  Purchase #5 $84.90   10.156%   $93.5224   $93.52   $93.50   $93.50  
  Purchase #6 $228.68   6.274%   $243.0274   $243.03   $243.05   $243.00  
  Purchase #7 $237.51   6.546%   $253.0574   $253.06   $253.05   $253.10  
  7 purchase totals = $857.53       $915.9634   $915.96   $915.95   $915.90