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 $60.79   10.726%   $67.3103   $67.31   $67.30   $67.30  
  Purchase #2 $154.62   8.108%   $167.1566   $167.16   $167.15   $167.20  
  Purchase #3 $133.96   11.693%   $149.6239   $149.62   $149.60   $149.60  
  Purchase #4 $235.40   8.845%   $256.2211   $256.22   $256.20   $256.20  
  Purchase #5 $219.50   6.471%   $233.7038   $233.70   $233.70   $233.70  
  Purchase #6 $154.91   8.191%   $167.5987   $167.60   $167.60   $167.60  
  Purchase #7 $191.55   6.795%   $204.5658   $204.57   $204.55   $204.60  
  7 purchase totals = $1,150.73       $1,246.1802   $1,246.18   $1,246.10   $1,246.20