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 $40.76   8.654%   $44.2874   $44.29   $44.30   $44.30  
  Purchase #2 $167.53   5.257%   $176.3371   $176.34   $176.35   $176.30  
  Purchase #3 $193.43   6.602%   $206.2002   $206.20   $206.20   $206.20  
  Purchase #4 $88.52   4.321%   $92.3449   $92.34   $92.35   $92.30  
  Purchase #5 $219.43   12.714%   $247.3283   $247.33   $247.35   $247.30  
  Purchase #6 $216.54   11.861%   $242.2238   $242.22   $242.20   $242.20  
  Purchase #7 $26.94   4.596%   $28.1782   $28.18   $28.20   $28.20  
  7 purchase totals = $953.15       $1,036.8999   $1,036.90   $1,036.95   $1,036.80