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 $174.95   10.347%   $193.0521   $193.05   $193.05   $193.10  
  Purchase #2 $160.51   4.449%   $167.6511   $167.65   $167.65   $167.70  
  Purchase #3 $118.41   13.428%   $134.3101   $134.31   $134.30   $134.30  
  Purchase #4 $74.37   4.694%   $77.8609   $77.86   $77.85   $77.90  
  Purchase #5 $99.72   11.529%   $111.2167   $111.22   $111.20   $111.20  
  Purchase #6 $87.46   8.570%   $94.9553   $94.96   $94.95   $95.00  
  Purchase #7 $22.40   10.763%   $24.8109   $24.81   $24.80   $24.80  
  7 purchase totals = $737.82       $803.8571   $803.86   $803.80   $804.00