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 $247.29   11.474%   $275.6641   $275.66   $275.65   $275.70  
  Purchase #2 $163.60   9.146%   $178.5629   $178.56   $178.55   $178.60  
  Purchase #3 $144.30   6.445%   $153.6001   $153.60   $153.60   $153.60  
  Purchase #4 $245.67   6.149%   $260.7762   $260.78   $260.80   $260.80  
  Purchase #5 $91.26   4.376%   $95.2535   $95.25   $95.25   $95.30  
  Purchase #6 $232.46   7.108%   $248.9833   $248.98   $249.00   $249.00  
  Purchase #7 $151.31   4.324%   $157.8526   $157.85   $157.85   $157.90  
  7 purchase totals = $1,275.89       $1,370.6927   $1,370.68   $1,370.70   $1,370.90