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 $205.80   13.355%   $233.2846   $233.28   $233.30   $233.30  
  Purchase #2 $87.90   8.489%   $95.3618   $95.36   $95.35   $95.40  
  Purchase #3 $142.95   4.658%   $149.6086   $149.61   $149.60   $149.60  
  Purchase #4 $228.42   11.278%   $254.1812   $254.18   $254.20   $254.20  
  Purchase #5 $229.69   13.558%   $260.8314   $260.83   $260.85   $260.80  
  Purchase #6 $174.69   11.170%   $194.2029   $194.20   $194.20   $194.20  
  Purchase #7 $45.57   4.199%   $47.4835   $47.48   $47.50   $47.50  
  7 purchase totals = $1,115.02       $1,234.9540   $1,234.94   $1,235.00   $1,235.00