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 $205.82   9.406%   $225.1794   $225.18   $225.20   $225.20  
  Purchase #2 $140.32   7.363%   $150.6518   $150.65   $150.65   $150.70  
  Purchase #3 $111.61   9.707%   $122.444   $122.44   $122.45   $122.40  
  Purchase #4 $232.62   11.778%   $260.018   $260.02   $260.00   $260.00  
  Purchase #5 $224.61   6.287%   $238.7312   $238.73   $238.75   $238.70  
  Purchase #6 $88.35   10.484%   $97.6126   $97.61   $97.60   $97.60  
  Purchase #7 $88.86   5.279%   $93.5509   $93.55   $93.55   $93.60  
  7 purchase totals = $1,092.19       $1,188.1879   $1,188.18   $1,188.20   $1,188.20