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 $135.46   13.490%   $153.7336   $153.73   $153.75   $153.70  
  Purchase #2 $31.27   12.145%   $35.0677   $35.07   $35.05   $35.10  
  Purchase #3 $212.89   7.156%   $228.1244   $228.12   $228.10   $228.10  
  Purchase #4 $162.93   13.529%   $184.9728   $184.97   $184.95   $185.00  
  Purchase #5 $104.67   8.144%   $113.1943   $113.19   $113.20   $113.20  
  Purchase #6 $249.46   9.436%   $272.999   $273.00   $273.00   $273.00  
  Purchase #7 $60.82   7.242%   $65.2246   $65.22   $65.20   $65.20  
  7 purchase totals = $957.50       $1,053.3164   $1,053.30   $1,053.25   $1,053.30