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 $220.61   11.827%   $246.7015   $246.70   $246.70   $246.70  
  Purchase #2 $35.43   11.752%   $39.5937   $39.59   $39.60   $39.60  
  Purchase #3 $52.41   4.146%   $54.5829   $54.58   $54.60   $54.60  
  Purchase #4 $56.94   12.121%   $63.8417   $63.84   $63.85   $63.80  
  Purchase #5 $218.65   12.135%   $245.1832   $245.18   $245.20   $245.20  
  Purchase #6 $62.52   12.698%   $70.4588   $70.46   $70.45   $70.50  
  Purchase #7 $165.90   4.842%   $173.9329   $173.93   $173.95   $173.90  
  7 purchase totals = $812.46       $894.2947   $894.28   $894.35   $894.30