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 $54.67   3.653%   $56.6671   $56.67   $56.65   $56.70  
  Purchase #2 $162.51   4.839%   $170.3739   $170.37   $170.35   $170.40  
  Purchase #3 $201.60   11.847%   $225.4836   $225.48   $225.50   $225.50  
  Purchase #4 $110.28   7.296%   $118.326   $118.33   $118.35   $118.30  
  Purchase #5 $113.29   13.843%   $128.9727   $128.97   $128.95   $129.00  
  Purchase #6 $116.92   10.173%   $128.8143   $128.81   $128.80   $128.80  
  Purchase #7 $88.27   5.848%   $93.432   $93.43   $93.45   $93.40  
  7 purchase totals = $847.54       $922.0696   $922.06   $922.05   $922.10