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 $237.54   3.658%   $246.2292   $246.23   $246.25   $246.20  
  Purchase #2 $13.65   5.744%   $14.4341   $14.43   $14.45   $14.40  
  Purchase #3 $180.68   3.441%   $186.8972   $186.90   $186.90   $186.90  
  Purchase #4 $19.38   6.593%   $20.6577   $20.66   $20.65   $20.70  
  Purchase #5 $138.40   11.224%   $153.934   $153.93   $153.95   $153.90  
  Purchase #6 $39.77   10.434%   $43.9196   $43.92   $43.90   $43.90  
  Purchase #7 $189.31   6.708%   $202.0089   $202.01   $202.00   $202.00  
  7 purchase totals = $818.73       $868.0807   $868.08   $868.10   $868.00