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 $32.79   7.743%   $35.3289   $35.33   $35.35   $35.30  
  Purchase #2 $62.72   11.378%   $69.8563   $69.86   $69.85   $69.90  
  Purchase #3 $195.43   12.857%   $220.5564   $220.56   $220.55   $220.60  
  Purchase #4 $131.71   7.449%   $141.5211   $141.52   $141.50   $141.50  
  Purchase #5 $203.95   13.368%   $231.214   $231.21   $231.20   $231.20  
  Purchase #6 $163.91   10.869%   $181.7254   $181.73   $181.75   $181.70  
  Purchase #7 $53.40   4.297%   $55.6946   $55.69   $55.70   $55.70  
  7 purchase totals = $843.91       $935.8967   $935.90   $935.90   $935.90