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 $192.66   10.661%   $213.1995   $213.20   $213.20   $213.20  
  Purchase #2 $53.78   5.457%   $56.7148   $56.71   $56.70   $56.70  
  Purchase #3 $27.75   7.376%   $29.7968   $29.80   $29.80   $29.80  
  Purchase #4 $62.35   10.689%   $69.0146   $69.01   $69.00   $69.00  
  Purchase #5 $61.40   6.711%   $65.5206   $65.52   $65.50   $65.50  
  Purchase #6 $108.32   4.557%   $113.2561   $113.26   $113.25   $113.30  
  Purchase #7 $53.84   5.290%   $56.6881   $56.69   $56.70   $56.70  
  7 purchase totals = $560.10       $604.1905   $604.19   $604.15   $604.20