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 $166.48   7.468%   $178.9127   $178.91   $178.90   $178.90  
  Purchase #2 $139.96   13.832%   $159.3193   $159.32   $159.30   $159.30  
  Purchase #3 $88.64   11.868%   $99.1598   $99.16   $99.15   $99.20  
  Purchase #4 $66.85   10.184%   $73.658   $73.66   $73.65   $73.70  
  Purchase #5 $139.77   5.494%   $147.449   $147.45   $147.45   $147.40  
  Purchase #6 $182.47   10.498%   $201.6257   $201.63   $201.65   $201.60  
  Purchase #7 $171.98   7.447%   $184.7874   $184.79   $184.80   $184.80  
  7 purchase totals = $956.15       $1,044.9119   $1,044.92   $1,044.90   $1,044.90