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 $134.50   5.558%   $141.9755   $141.98   $142.00   $142.00  
  Purchase #2 $97.95   4.469%   $102.3274   $102.33   $102.35   $102.30  
  Purchase #3 $216.63   9.765%   $237.7839   $237.78   $237.80   $237.80  
  Purchase #4 $24.73   12.463%   $27.8121   $27.81   $27.80   $27.80  
  Purchase #5 $66.80   5.229%   $70.293   $70.29   $70.30   $70.30  
  Purchase #6 $73.79   5.150%   $77.5902   $77.59   $77.60   $77.60  
  Purchase #7 $97.46   5.245%   $102.5718   $102.57   $102.55   $102.60  
  7 purchase totals = $711.86       $760.3539   $760.35   $760.40   $760.40