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 $69.90   11.526%   $77.9567   $77.96   $77.95   $78.00  
  Purchase #2 $80.61   12.189%   $90.4356   $90.44   $90.45   $90.40  
  Purchase #3 $29.46   11.341%   $32.8011   $32.80   $32.80   $32.80  
  Purchase #4 $204.73   12.432%   $230.182   $230.18   $230.20   $230.20  
  Purchase #5 $115.55   5.138%   $121.487   $121.49   $121.50   $121.50  
  Purchase #6 $116.73   11.669%   $130.3512   $130.35   $130.35   $130.40  
  Purchase #7 $218.27   11.678%   $243.7596   $243.76   $243.75   $243.80  
  7 purchase totals = $835.25       $926.9732   $926.98   $927.00   $927.10