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 $104.32   3.642%   $108.1193   $108.12   $108.10   $108.10  
  Purchase #2 $226.98   12.794%   $256.0198   $256.02   $256.00   $256.00  
  Purchase #3 $6.42   12.777%   $7.2403   $7.24   $7.25   $7.20  
  Purchase #4 $96.52   7.394%   $103.6567   $103.66   $103.65   $103.70  
  Purchase #5 $124.58   11.278%   $138.6301   $138.63   $138.65   $138.60  
  Purchase #6 $200.39   4.503%   $209.4136   $209.41   $209.40   $209.40  
  Purchase #7 $174.75   9.775%   $191.8318   $191.83   $191.85   $191.80  
  7 purchase totals = $933.96       $1,014.9116   $1,014.91   $1,014.90   $1,014.80