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 $58.48   10.559%   $64.6549   $64.65   $64.65   $64.70  
  Purchase #2 $12.99   5.166%   $13.6611   $13.66   $13.65   $13.70  
  Purchase #3 $84.93   12.786%   $95.7891   $95.79   $95.80   $95.80  
  Purchase #4 $6.25   9.731%   $6.8582   $6.86   $6.85   $6.90  
  Purchase #5 $115.72   11.323%   $128.823   $128.82   $128.80   $128.80  
  Purchase #6 $39.52   3.740%   $40.998   $41.00   $41.00   $41.00  
  Purchase #7 $29.34   5.331%   $30.9041   $30.90   $30.90   $30.90  
  7 purchase totals = $347.23       $381.6884   $381.68   $381.65   $381.80