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 $243.80   9.777%   $267.6363   $267.64   $267.65   $267.60  
  Purchase #2 $202.97   3.633%   $210.3439   $210.34   $210.35   $210.30  
  Purchase #3 $74.40   4.231%   $77.5479   $77.55   $77.55   $77.50  
  Purchase #4 $198.99   11.216%   $221.3087   $221.31   $221.30   $221.30  
  Purchase #5 $226.90   7.417%   $243.7292   $243.73   $243.75   $243.70  
  Purchase #6 $200.33   12.473%   $225.3172   $225.32   $225.30   $225.30  
  Purchase #7 $118.66   8.229%   $128.4245   $128.42   $128.40   $128.40  
  7 purchase totals = $1,266.05       $1,374.3077   $1,374.31   $1,374.30   $1,374.10