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 $88.76   9.511%   $97.202   $97.20   $97.20   $97.20  
  Purchase #2 $197.93   3.753%   $205.3583   $205.36   $205.35   $205.40  
  Purchase #3 $53.33   5.752%   $56.3975   $56.40   $56.40   $56.40  
  Purchase #4 $16.61   6.579%   $17.7028   $17.70   $17.70   $17.70  
  Purchase #5 $129.97   11.529%   $144.9542   $144.95   $144.95   $145.00  
  Purchase #6 $226.44   6.624%   $241.4394   $241.44   $241.45   $241.40  
  Purchase #7 $197.49   12.672%   $222.5159   $222.52   $222.50   $222.50  
  7 purchase totals = $910.53       $985.5701   $985.57   $985.55   $985.60