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 $227.34   8.329%   $246.2751   $246.28   $246.30   $246.30  
  Purchase #2 $190.39   7.633%   $204.9225   $204.92   $204.90   $204.90  
  Purchase #3 $49.70   11.669%   $55.4995   $55.50   $55.50   $55.50  
  Purchase #4 $209.41   11.131%   $232.7194   $232.72   $232.70   $232.70  
  Purchase #5 $80.47   8.250%   $87.1088   $87.11   $87.10   $87.10  
  Purchase #6 $133.55   5.591%   $141.0168   $141.02   $141.00   $141.00  
  Purchase #7 $91.31   11.192%   $101.5294   $101.53   $101.55   $101.50  
  7 purchase totals = $982.17       $1,069.0715   $1,069.08   $1,069.05   $1,069.00