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 $31.34   11.396%   $34.9115   $34.91   $34.90   $34.90  
  Purchase #2 $164.95   3.184%   $170.202   $170.20   $170.20   $170.20  
  Purchase #3 $95.97   5.653%   $101.3952   $101.40   $101.40   $101.40  
  Purchase #4 $88.72   3.376%   $91.7152   $91.72   $91.70   $91.70  
  Purchase #5 $249.85   7.219%   $267.8867   $267.89   $267.90   $267.90  
  Purchase #6 $238.56   6.809%   $254.8036   $254.80   $254.80   $254.80  
  Purchase #7 $111.87   11.492%   $124.7261   $124.73   $124.75   $124.70  
  7 purchase totals = $981.26       $1,045.6403   $1,045.65   $1,045.65   $1,045.60