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 $231.87   4.416%   $242.1094   $242.11   $242.10   $242.10  
  Purchase #2 $142.25   13.342%   $161.229   $161.23   $161.25   $161.20  
  Purchase #3 $98.40   12.351%   $110.5534   $110.55   $110.55   $110.60  
  Purchase #4 $91.85   10.395%   $101.3978   $101.40   $101.40   $101.40  
  Purchase #5 $126.52   10.681%   $140.0336   $140.03   $140.05   $140.00  
  Purchase #6 $219.62   8.737%   $238.8082   $238.81   $238.80   $238.80  
  Purchase #7 $102.38   6.427%   $108.96   $108.96   $108.95   $109.00  
  7 purchase totals = $1,012.89       $1,103.0914   $1,103.09   $1,103.10   $1,103.10