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 $66.44   4.741%   $69.5899   $69.59   $69.60   $69.60  
  Purchase #2 $196.64   6.669%   $209.7539   $209.75   $209.75   $209.80  
  Purchase #3 $193.70   4.731%   $202.8639   $202.86   $202.85   $202.90  
  Purchase #4 $157.56   10.418%   $173.9746   $173.97   $173.95   $174.00  
  Purchase #5 $235.26   6.874%   $251.4318   $251.43   $251.45   $251.40  
  Purchase #6 $153.28   9.209%   $167.3956   $167.40   $167.40   $167.40  
  Purchase #7 $56.60   11.160%   $62.9166   $62.92   $62.90   $62.90  
  7 purchase totals = $1,059.48       $1,137.9263   $1,137.92   $1,137.90   $1,138.00