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 $180.34   8.278%   $195.2685   $195.27   $195.25   $195.30  
  Purchase #2 $27.85   4.360%   $29.0643   $29.06   $29.05   $29.10  
  Purchase #3 $151.36   11.560%   $168.8572   $168.86   $168.85   $168.90  
  Purchase #4 $58.71   9.582%   $64.3356   $64.34   $64.35   $64.30  
  Purchase #5 $183.85   8.668%   $199.7861   $199.79   $199.80   $199.80  
  Purchase #6 $112.70   8.816%   $122.6356   $122.64   $122.65   $122.60  
  Purchase #7 $59.63   9.523%   $65.3086   $65.31   $65.30   $65.30  
  7 purchase totals = $774.44       $845.2559   $845.27   $845.25   $845.30