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 $60.42   9.208%   $65.9835   $65.98   $66.00   $66.00  
  Purchase #2 $34.63   6.852%   $37.0028   $37.00   $37.00   $37.00  
  Purchase #3 $142.72   9.121%   $155.7375   $155.74   $155.75   $155.70  
  Purchase #4 $23.86   6.711%   $25.4612   $25.46   $25.45   $25.50  
  Purchase #5 $106.76   11.850%   $119.4111   $119.41   $119.40   $119.40  
  Purchase #6 $244.92   12.397%   $275.2827   $275.28   $275.30   $275.30  
  Purchase #7 $217.67   12.194%   $244.2127   $244.21   $244.20   $244.20  
  7 purchase totals = $830.98       $923.0915   $923.08   $923.10   $923.10