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 $44.96   5.306%   $47.3456   $47.35   $47.35   $47.30  
  Purchase #2 $211.81   12.572%   $238.4388   $238.44   $238.45   $238.40  
  Purchase #3 $154.75   11.693%   $172.8449   $172.84   $172.85   $172.80  
  Purchase #4 $239.43   13.394%   $271.4993   $271.50   $271.50   $271.50  
  Purchase #5 $218.32   10.157%   $240.4948   $240.49   $240.50   $240.50  
  Purchase #6 $103.74   6.736%   $110.7279   $110.73   $110.75   $110.70  
  Purchase #7 $201.70   5.314%   $212.4183   $212.42   $212.40   $212.40  
  7 purchase totals = $1,174.71       $1,293.7696   $1,293.77   $1,293.80   $1,293.60