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 $246.32   9.275%   $269.1662   $269.17   $269.15   $269.20  
  Purchase #2 $75.35   12.287%   $84.6083   $84.61   $84.60   $84.60  
  Purchase #3 $235.68   10.200%   $259.7194   $259.72   $259.70   $259.70  
  Purchase #4 $43.64   6.147%   $46.3226   $46.32   $46.30   $46.30  
  Purchase #5 $134.94   11.222%   $150.083   $150.08   $150.10   $150.10  
  Purchase #6 $30.81   11.117%   $34.2351   $34.24   $34.25   $34.20  
  Purchase #7 $44.31   8.623%   $48.1309   $48.13   $48.15   $48.10  
  7 purchase totals = $811.05       $892.2655   $892.27   $892.25   $892.20