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 $105.79   12.262%   $118.762   $118.76   $118.75   $118.80  
  Purchase #2 $212.35   12.626%   $239.1613   $239.16   $239.15   $239.20  
  Purchase #3 $77.34   13.543%   $87.8142   $87.81   $87.80   $87.80  
  Purchase #4 $225.42   11.149%   $250.5521   $250.55   $250.55   $250.60  
  Purchase #5 $94.30   10.241%   $103.9573   $103.96   $103.95   $104.00  
  Purchase #6 $108.91   10.563%   $120.4142   $120.41   $120.40   $120.40  
  Purchase #7 $109.57   3.290%   $113.1749   $113.17   $113.15   $113.20  
  7 purchase totals = $933.68       $1,033.8360   $1,033.82   $1,033.75   $1,034.00