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 $35.92   8.260%   $38.887   $38.89   $38.90   $38.90  
  Purchase #2 $106.29   3.217%   $109.7093   $109.71   $109.70   $109.70  
  Purchase #3 $180.78   13.200%   $204.643   $204.64   $204.65   $204.60  
  Purchase #4 $241.96   13.530%   $274.6972   $274.70   $274.70   $274.70  
  Purchase #5 $250.76   7.307%   $269.083   $269.08   $269.10   $269.10  
  Purchase #6 $56.82   3.131%   $58.599   $58.60   $58.60   $58.60  
  Purchase #7 $98.86   8.805%   $107.5646   $107.56   $107.55   $107.60  
  7 purchase totals = $971.39       $1,063.1831   $1,063.18   $1,063.20   $1,063.20