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 $84.91   9.870%   $93.2906   $93.29   $93.30   $93.30  
  Purchase #2 $161.37   8.271%   $174.7169   $174.72   $174.70   $174.70  
  Purchase #3 $104.95   12.455%   $118.0215   $118.02   $118.00   $118.00  
  Purchase #4 $21.55   12.410%   $24.2244   $24.22   $24.20   $24.20  
  Purchase #5 $104.95   4.827%   $110.0159   $110.02   $110.00   $110.00  
  Purchase #6 $244.56   7.813%   $263.6675   $263.67   $263.65   $263.70  
  Purchase #7 $151.90   12.702%   $171.1943   $171.19   $171.20   $171.20  
  7 purchase totals = $874.19       $955.1311   $955.13   $955.05   $955.10