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 $139.68   11.505%   $155.7502   $155.75   $155.75   $155.80  
  Purchase #2 $154.66   10.476%   $170.8622   $170.86   $170.85   $170.90  
  Purchase #3 $11.53   9.852%   $12.6659   $12.67   $12.65   $12.70  
  Purchase #4 $71.64   6.807%   $76.5165   $76.52   $76.50   $76.50  
  Purchase #5 $39.98   4.715%   $41.8651   $41.87   $41.85   $41.90  
  Purchase #6 $197.97   3.307%   $204.5169   $204.52   $204.50   $204.50  
  Purchase #7 $38.65   7.641%   $41.6032   $41.60   $41.60   $41.60  
  7 purchase totals = $654.11       $703.7800   $703.79   $703.70   $703.90