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 $63.59   7.339%   $68.2569   $68.26   $68.25   $68.30  
  Purchase #2 $143.57   6.442%   $152.8188   $152.82   $152.80   $152.80  
  Purchase #3 $218.30   10.179%   $240.5208   $240.52   $240.50   $240.50  
  Purchase #4 $232.47   13.198%   $263.1514   $263.15   $263.15   $263.20  
  Purchase #5 $59.50   8.662%   $64.6539   $64.65   $64.65   $64.70  
  Purchase #6 $202.86   11.442%   $226.0712   $226.07   $226.05   $226.10  
  Purchase #7 $29.90   13.862%   $34.0447   $34.04   $34.05   $34.00  
  7 purchase totals = $950.19       $1,049.5177   $1,049.51   $1,049.45   $1,049.60