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 $60.69   5.781%   $64.1985   $64.20   $64.20   $64.20  
  Purchase #2 $206.78   6.615%   $220.4585   $220.46   $220.45   $220.50  
  Purchase #3 $81.55   8.758%   $88.6921   $88.69   $88.70   $88.70  
  Purchase #4 $154.53   3.407%   $159.7948   $159.79   $159.80   $159.80  
  Purchase #5 $212.70   3.846%   $220.8804   $220.88   $220.90   $220.90  
  Purchase #6 $128.71   5.743%   $136.1018   $136.10   $136.10   $136.10  
  Purchase #7 $236.49   6.187%   $251.1216   $251.12   $251.10   $251.10  
  7 purchase totals = $1,081.45       $1,141.2477   $1,141.24   $1,141.25   $1,141.30