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 $84.65   11.714%   $94.5659   $94.57   $94.55   $94.60  
  Purchase #2 $56.70   10.496%   $62.6512   $62.65   $62.65   $62.70  
  Purchase #3 $96.99   6.492%   $103.2866   $103.29   $103.30   $103.30  
  Purchase #4 $228.99   13.577%   $260.08   $260.08   $260.10   $260.10  
  Purchase #5 $49.44   6.445%   $52.6264   $52.63   $52.65   $52.60  
  Purchase #6 $42.90   4.235%   $44.7168   $44.72   $44.70   $44.70  
  Purchase #7 $111.49   10.549%   $123.2511   $123.25   $123.25   $123.30  
  7 purchase totals = $671.16       $741.1780   $741.19   $741.20   $741.30