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 $56.58   5.446%   $59.6613   $59.66   $59.65   $59.70  
  Purchase #2 $230.52   4.273%   $240.3701   $240.37   $240.35   $240.40  
  Purchase #3 $174.84   8.403%   $189.5318   $189.53   $189.55   $189.50  
  Purchase #4 $194.74   4.857%   $204.1985   $204.20   $204.20   $204.20  
  Purchase #5 $8.49   10.786%   $9.4057   $9.41   $9.40   $9.40  
  Purchase #6 $71.91   5.619%   $75.9506   $75.95   $75.95   $76.00  
  Purchase #7 $5.72   11.813%   $6.3957   $6.40   $6.40   $6.40  
  7 purchase totals = $742.80       $785.5137   $785.52   $785.50   $785.60