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 $66.66   3.791%   $69.1871   $69.19   $69.20   $69.20  
  Purchase #2 $22.81   11.563%   $25.4475   $25.45   $25.45   $25.40  
  Purchase #3 $106.81   13.746%   $121.4921   $121.49   $121.50   $121.50  
  Purchase #4 $231.31   7.780%   $249.3059   $249.31   $249.30   $249.30  
  Purchase #5 $226.42   4.730%   $237.1297   $237.13   $237.15   $237.10  
  Purchase #6 $191.51   9.454%   $209.6154   $209.62   $209.60   $209.60  
  Purchase #7 $152.75   9.851%   $167.7974   $167.80   $167.80   $167.80  
  7 purchase totals = $998.27       $1,079.9751   $1,079.99   $1,080.00   $1,079.90