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 $40.43   13.108%   $45.7296   $45.73   $45.75   $45.70  
  Purchase #2 $226.47   11.505%   $252.5254   $252.53   $252.55   $252.50  
  Purchase #3 $201.36   11.685%   $224.8889   $224.89   $224.90   $224.90  
  Purchase #4 $163.83   6.588%   $174.6231   $174.62   $174.60   $174.60  
  Purchase #5 $185.90   9.713%   $203.9565   $203.96   $203.95   $204.00  
  Purchase #6 $244.98   13.656%   $278.4345   $278.43   $278.45   $278.40  
  Purchase #7 $146.59   13.319%   $166.1143   $166.11   $166.10   $166.10  
  7 purchase totals = $1,209.56       $1,346.2723   $1,346.27   $1,346.30   $1,346.20