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 $212.64   12.207%   $238.597   $238.60   $238.60   $238.60  
  Purchase #2 $114.79   5.293%   $120.8658   $120.87   $120.85   $120.90  
  Purchase #3 $115.77   11.393%   $128.9597   $128.96   $128.95   $129.00  
  Purchase #4 $228.51   3.109%   $235.6144   $235.61   $235.60   $235.60  
  Purchase #5 $58.84   10.158%   $64.817   $64.82   $64.80   $64.80  
  Purchase #6 $143.30   4.282%   $149.4361   $149.44   $149.45   $149.40  
  Purchase #7 $222.37   6.431%   $236.6706   $236.67   $236.65   $236.70  
  7 purchase totals = $1,096.22       $1,174.9606   $1,174.97   $1,174.90   $1,175.00