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 $232.27   6.212%   $246.6986   $246.70   $246.70   $246.70  
  Purchase #2 $138.82   11.337%   $154.558   $154.56   $154.55   $154.60  
  Purchase #3 $167.64   6.173%   $177.9884   $177.99   $178.00   $178.00  
  Purchase #4 $100.94   8.327%   $109.3453   $109.35   $109.35   $109.30  
  Purchase #5 $225.63   6.120%   $239.4386   $239.44   $239.45   $239.40  
  Purchase #6 $45.53   11.669%   $50.8429   $50.84   $50.85   $50.80  
  Purchase #7 $53.48   9.444%   $58.5307   $58.53   $58.55   $58.50  
  7 purchase totals = $964.31       $1,037.4025   $1,037.41   $1,037.45   $1,037.30