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 $149.64   5.244%   $157.4871   $157.49   $157.50   $157.50  
  Purchase #2 $14.59   11.770%   $16.3072   $16.31   $16.30   $16.30  
  Purchase #3 $109.72   10.568%   $121.3152   $121.32   $121.30   $121.30  
  Purchase #4 $20.98   5.758%   $22.188   $22.19   $22.20   $22.20  
  Purchase #5 $154.69   10.594%   $171.0779   $171.08   $171.10   $171.10  
  Purchase #6 $90.57   4.642%   $94.7743   $94.77   $94.75   $94.80  
  Purchase #7 $30.70   3.119%   $31.6575   $31.66   $31.65   $31.70  
  7 purchase totals = $570.89       $614.8072   $614.82   $614.80   $614.90