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 $168.75   9.374%   $184.5686   $184.57   $184.55   $184.60  
  Purchase #2 $55.55   5.180%   $58.4275   $58.43   $58.45   $58.40  
  Purchase #3 $69.67   10.674%   $77.1066   $77.11   $77.10   $77.10  
  Purchase #4 $87.99   5.762%   $93.06   $93.06   $93.05   $93.10  
  Purchase #5 $63.71   8.478%   $69.1113   $69.11   $69.10   $69.10  
  Purchase #6 $183.46   11.664%   $204.8588   $204.86   $204.85   $204.90  
  Purchase #7 $135.80   8.623%   $147.51   $147.51   $147.50   $147.50  
  7 purchase totals = $764.93       $834.6428   $834.65   $834.60   $834.70