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 $234.74   5.546%   $247.7587   $247.76   $247.75   $247.80  
  Purchase #2 $138.41   13.514%   $157.1147   $157.11   $157.10   $157.10  
  Purchase #3 $216.43   11.165%   $240.5944   $240.59   $240.60   $240.60  
  Purchase #4 $219.47   3.340%   $226.8003   $226.80   $226.80   $226.80  
  Purchase #5 $134.84   9.266%   $147.3343   $147.33   $147.35   $147.30  
  Purchase #6 $90.54   13.211%   $102.5012   $102.50   $102.50   $102.50  
  Purchase #7 $60.60   9.755%   $66.5115   $66.51   $66.50   $66.50  
  7 purchase totals = $1,095.03       $1,188.6151   $1,188.60   $1,188.60   $1,188.60