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 $48.31   11.760%   $53.9913   $53.99   $54.00   $54.00  
  Purchase #2 $152.85   8.799%   $166.2993   $166.30   $166.30   $166.30  
  Purchase #3 $67.30   3.620%   $69.7363   $69.74   $69.75   $69.70  
  Purchase #4 $221.84   13.760%   $252.3652   $252.37   $252.35   $252.40  
  Purchase #5 $244.58   3.355%   $252.7857   $252.79   $252.80   $252.80  
  Purchase #6 $114.50   5.767%   $121.1032   $121.10   $121.10   $121.10  
  Purchase #7 $11.75   13.416%   $13.3264   $13.33   $13.35   $13.30  
  7 purchase totals = $861.13       $929.6074   $929.62   $929.65   $929.60