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 $42.81   4.729%   $44.8345   $44.83   $44.85   $44.80  
  Purchase #2 $147.68   13.519%   $167.6449   $167.64   $167.65   $167.60  
  Purchase #3 $239.54   4.170%   $249.5288   $249.53   $249.55   $249.50  
  Purchase #4 $227.84   12.648%   $256.6572   $256.66   $256.65   $256.70  
  Purchase #5 $80.86   5.315%   $85.1577   $85.16   $85.15   $85.20  
  Purchase #6 $60.79   9.346%   $66.4714   $66.47   $66.45   $66.50  
  Purchase #7 $171.88   6.591%   $183.2086   $183.21   $183.20   $183.20  
  7 purchase totals = $971.40       $1,053.5031   $1,053.50   $1,053.50   $1,053.50