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 $98.76   13.113%   $111.7104   $111.71   $111.70   $111.70  
  Purchase #2 $232.85   5.121%   $244.7742   $244.77   $244.75   $244.80  
  Purchase #3 $167.85   6.215%   $178.2819   $178.28   $178.30   $178.30  
  Purchase #4 $44.45   7.479%   $47.7744   $47.77   $47.75   $47.80  
  Purchase #5 $118.29   5.685%   $125.0148   $125.01   $125.00   $125.00  
  Purchase #6 $157.97   5.119%   $166.0565   $166.06   $166.05   $166.10  
  Purchase #7 $134.97   11.843%   $150.9545   $150.95   $150.95   $151.00  
  7 purchase totals = $955.14       $1,024.5667   $1,024.55   $1,024.50   $1,024.70