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 $119.77   7.719%   $129.015   $129.02   $129.00   $129.00  
  Purchase #2 $51.82   7.458%   $55.6847   $55.68   $55.70   $55.70  
  Purchase #3 $210.66   12.638%   $237.2832   $237.28   $237.30   $237.30  
  Purchase #4 $236.84   7.459%   $254.5059   $254.51   $254.50   $254.50  
  Purchase #5 $103.77   6.263%   $110.2691   $110.27   $110.25   $110.30  
  Purchase #6 $198.82   4.544%   $207.8544   $207.85   $207.85   $207.90  
  Purchase #7 $34.90   11.566%   $38.9365   $38.94   $38.95   $38.90  
  7 purchase totals = $956.58       $1,033.5488   $1,033.55   $1,033.55   $1,033.60