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 $61.67   11.649%   $68.8539   $68.85   $68.85   $68.90  
  Purchase #2 $219.89   11.288%   $244.7112   $244.71   $244.70   $244.70  
  Purchase #3 $9.67   10.342%   $10.6701   $10.67   $10.65   $10.70  
  Purchase #4 $167.86   11.464%   $187.1035   $187.10   $187.10   $187.10  
  Purchase #5 $45.99   4.658%   $48.1322   $48.13   $48.15   $48.10  
  Purchase #6 $66.27   4.325%   $69.1362   $69.14   $69.15   $69.10  
  Purchase #7 $205.73   6.284%   $218.6581   $218.66   $218.65   $218.70  
  7 purchase totals = $777.08       $847.2652   $847.26   $847.25   $847.30