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 $203.93   11.154%   $226.6764   $226.68   $226.70   $226.70  
  Purchase #2 $52.91   11.838%   $59.1735   $59.17   $59.15   $59.20  
  Purchase #3 $174.26   9.407%   $190.6526   $190.65   $190.65   $190.70  
  Purchase #4 $183.62   11.127%   $204.0514   $204.05   $204.05   $204.10  
  Purchase #5 $23.32   10.199%   $25.6984   $25.70   $25.70   $25.70  
  Purchase #6 $32.45   5.660%   $34.2867   $34.29   $34.30   $34.30  
  Purchase #7 $205.27   9.539%   $224.8507   $224.85   $224.85   $224.90  
  7 purchase totals = $875.76       $965.3897   $965.39   $965.40   $965.60