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 $38.68   6.198%   $41.0774   $41.08   $41.10   $41.10  
  Purchase #2 $65.45   11.642%   $73.0697   $73.07   $73.05   $73.10  
  Purchase #3 $52.25   8.821%   $56.859   $56.86   $56.85   $56.90  
  Purchase #4 $207.87   8.179%   $224.8717   $224.87   $224.85   $224.90  
  Purchase #5 $121.95   11.530%   $136.0108   $136.01   $136.00   $136.00  
  Purchase #6 $214.43   12.667%   $241.5918   $241.59   $241.60   $241.60  
  Purchase #7 $24.55   4.240%   $25.5909   $25.59   $25.60   $25.60  
  7 purchase totals = $725.18       $799.0713   $799.07   $799.05   $799.20