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 $56.90   7.468%   $61.1493   $61.15   $61.15   $61.10  
  Purchase #2 $42.84   3.848%   $44.4885   $44.49   $44.50   $44.50  
  Purchase #3 $17.92   6.332%   $19.0547   $19.05   $19.05   $19.10  
  Purchase #4 $153.38   10.469%   $169.4374   $169.44   $169.45   $169.40  
  Purchase #5 $53.57   6.855%   $57.2422   $57.24   $57.25   $57.20  
  Purchase #6 $202.57   13.302%   $229.5159   $229.52   $229.50   $229.50  
  Purchase #7 $204.58   10.196%   $225.439   $225.44   $225.45   $225.40  
  7 purchase totals = $731.76       $806.3270   $806.33   $806.35   $806.20