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 $31.75   8.183%   $34.3481   $34.35   $34.35   $34.30  
  Purchase #2 $235.28   4.835%   $246.6558   $246.66   $246.65   $246.70  
  Purchase #3 $217.81   8.521%   $236.3696   $236.37   $236.35   $236.40  
  Purchase #4 $143.34   6.826%   $153.1244   $153.12   $153.10   $153.10  
  Purchase #5 $20.33   13.392%   $23.0526   $23.05   $23.05   $23.10  
  Purchase #6 $228.79   4.194%   $238.3855   $238.39   $238.40   $238.40  
  Purchase #7 $85.90   10.266%   $94.7185   $94.72   $94.70   $94.70  
  7 purchase totals = $963.20       $1,026.6545   $1,026.66   $1,026.60   $1,026.70