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 $162.29   12.549%   $182.6558   $182.66   $182.65   $182.70  
  Purchase #2 $69.53   8.497%   $75.438   $75.44   $75.45   $75.40  
  Purchase #3 $98.88   3.753%   $102.591   $102.59   $102.60   $102.60  
  Purchase #4 $247.99   7.404%   $266.3512   $266.35   $266.35   $266.40  
  Purchase #5 $159.84   11.586%   $178.3591   $178.36   $178.35   $178.40  
  Purchase #6 $69.76   8.145%   $75.442   $75.44   $75.45   $75.40  
  Purchase #7 $225.77   8.716%   $245.4481   $245.45   $245.45   $245.40  
  7 purchase totals = $1,034.06       $1,126.2852   $1,126.29   $1,126.30   $1,126.30