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 $84.68   9.123%   $92.4054   $92.41   $92.40   $92.40  
  Purchase #2 $183.47   11.353%   $204.2993   $204.30   $204.30   $204.30  
  Purchase #3 $195.77   7.484%   $210.4214   $210.42   $210.40   $210.40  
  Purchase #4 $239.36   7.393%   $257.0559   $257.06   $257.05   $257.10  
  Purchase #5 $221.72   4.524%   $231.7506   $231.75   $231.75   $231.80  
  Purchase #6 $23.98   10.583%   $26.5178   $26.52   $26.50   $26.50  
  Purchase #7 $29.27   7.227%   $31.3853   $31.39   $31.40   $31.40  
  7 purchase totals = $978.25       $1,053.8357   $1,053.85   $1,053.80   $1,053.90