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 $10.53   13.471%   $11.9485   $11.95   $11.95   $11.90  
  Purchase #2 $167.35   6.801%   $178.7315   $178.73   $178.75   $178.70  
  Purchase #3 $184.96   10.828%   $204.9875   $204.99   $205.00   $205.00  
  Purchase #4 $82.77   12.366%   $93.0053   $93.01   $93.00   $93.00  
  Purchase #5 $98.37   3.522%   $101.8346   $101.83   $101.85   $101.80  
  Purchase #6 $233.39   11.521%   $260.2789   $260.28   $260.30   $260.30  
  Purchase #7 $233.50   4.119%   $243.1179   $243.12   $243.10   $243.10  
  7 purchase totals = $1,010.87       $1,093.9042   $1,093.91   $1,093.95   $1,093.80