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 $236.49   13.673%   $268.8253   $268.83   $268.85   $268.80  
  Purchase #2 $138.30   6.385%   $147.1305   $147.13   $147.15   $147.10  
  Purchase #3 $181.91   4.406%   $189.925   $189.93   $189.95   $189.90  
  Purchase #4 $194.68   9.155%   $212.503   $212.50   $212.50   $212.50  
  Purchase #5 $27.64   13.183%   $31.2838   $31.28   $31.30   $31.30  
  Purchase #6 $125.27   6.569%   $133.499   $133.50   $133.50   $133.50  
  Purchase #7 $191.50   9.460%   $209.6159   $209.62   $209.60   $209.60  
  7 purchase totals = $1,095.79       $1,192.7825   $1,192.79   $1,192.85   $1,192.70