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 $102.36   13.682%   $116.3649   $116.36   $116.35   $116.40  
  Purchase #2 $166.32   11.162%   $184.8846   $184.88   $184.90   $184.90  
  Purchase #3 $202.95   4.611%   $212.308   $212.31   $212.30   $212.30  
  Purchase #4 $245.43   13.808%   $279.319   $279.32   $279.30   $279.30  
  Purchase #5 $56.59   11.721%   $63.2229   $63.22   $63.20   $63.20  
  Purchase #6 $198.45   12.666%   $223.5857   $223.59   $223.60   $223.60  
  Purchase #7 $232.97   12.553%   $262.2147   $262.21   $262.20   $262.20  
  7 purchase totals = $1,205.07       $1,341.8998   $1,341.89   $1,341.85   $1,341.90