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 $67.41   10.760%   $74.6633   $74.66   $74.65   $74.70  
  Purchase #2 $243.33   9.560%   $266.5923   $266.59   $266.60   $266.60  
  Purchase #3 $157.98   5.395%   $166.503   $166.50   $166.50   $166.50  
  Purchase #4 $34.37   13.791%   $39.11   $39.11   $39.10   $39.10  
  Purchase #5 $245.88   5.470%   $259.3296   $259.33   $259.35   $259.30  
  Purchase #6 $145.78   5.265%   $153.4553   $153.46   $153.45   $153.50  
  Purchase #7 $223.87   7.672%   $241.0453   $241.05   $241.05   $241.00  
  7 purchase totals = $1,118.62       $1,200.6988   $1,200.70   $1,200.70   $1,200.70