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 $88.48   5.698%   $93.5216   $93.52   $93.50   $93.50  
  Purchase #2 $11.90   4.425%   $12.4266   $12.43   $12.45   $12.40  
  Purchase #3 $236.29   10.787%   $261.7786   $261.78   $261.80   $261.80  
  Purchase #4 $117.34   5.205%   $123.4475   $123.45   $123.45   $123.40  
  Purchase #5 $215.49   7.804%   $232.3068   $232.31   $232.30   $232.30  
  Purchase #6 $76.27   9.412%   $83.4485   $83.45   $83.45   $83.40  
  Purchase #7 $206.36   6.456%   $219.6826   $219.68   $219.70   $219.70  
  7 purchase totals = $952.13       $1,026.6122   $1,026.62   $1,026.65   $1,026.50