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 $80.77   8.123%   $87.3309   $87.33   $87.35   $87.30  
  Purchase #2 $195.42   3.519%   $202.2968   $202.30   $202.30   $202.30  
  Purchase #3 $98.46   8.199%   $106.5327   $106.53   $106.55   $106.50  
  Purchase #4 $247.49   8.213%   $267.8164   $267.82   $267.80   $267.80  
  Purchase #5 $154.74   6.871%   $165.3722   $165.37   $165.35   $165.40  
  Purchase #6 $172.34   10.402%   $190.2668   $190.27   $190.25   $190.30  
  Purchase #7 $23.93   9.471%   $26.1964   $26.20   $26.20   $26.20  
  7 purchase totals = $973.15       $1,045.8122   $1,045.82   $1,045.80   $1,045.80