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 $192.44   4.598%   $201.2884   $201.29   $201.30   $201.30  
  Purchase #2 $115.60   5.476%   $121.9303   $121.93   $121.95   $121.90  
  Purchase #3 $177.58   11.685%   $198.3302   $198.33   $198.35   $198.30  
  Purchase #4 $184.93   9.630%   $202.7388   $202.74   $202.75   $202.70  
  Purchase #5 $198.25   9.596%   $217.2741   $217.27   $217.25   $217.30  
  Purchase #6 $71.54   5.164%   $75.2343   $75.23   $75.25   $75.20  
  Purchase #7 $136.50   12.441%   $153.482   $153.48   $153.50   $153.50  
  7 purchase totals = $1,076.84       $1,170.2781   $1,170.27   $1,170.35   $1,170.20