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 $204.83   9.515%   $224.3196   $224.32   $224.30   $224.30  
  Purchase #2 $63.70   3.197%   $65.7365   $65.74   $65.75   $65.70  
  Purchase #3 $191.30   8.736%   $208.012   $208.01   $208.00   $208.00  
  Purchase #4 $209.91   12.223%   $235.5673   $235.57   $235.55   $235.60  
  Purchase #5 $153.31   7.230%   $164.3943   $164.39   $164.40   $164.40  
  Purchase #6 $228.46   12.222%   $256.3824   $256.38   $256.40   $256.40  
  Purchase #7 $101.29   5.497%   $106.8579   $106.86   $106.85   $106.90  
  7 purchase totals = $1,152.80       $1,261.2700   $1,261.27   $1,261.25   $1,261.30