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 $201.44   11.860%   $225.3308   $225.33   $225.35   $225.30  
  Purchase #2 $71.92   3.849%   $74.6882   $74.69   $74.70   $74.70  
  Purchase #3 $104.32   8.187%   $112.8607   $112.86   $112.85   $112.90  
  Purchase #4 $147.77   4.427%   $154.3118   $154.31   $154.30   $154.30  
  Purchase #5 $238.95   6.635%   $254.8043   $254.80   $254.80   $254.80  
  Purchase #6 $189.89   6.525%   $202.2803   $202.28   $202.30   $202.30  
  Purchase #7 $109.51   9.632%   $120.058   $120.06   $120.05   $120.10  
  7 purchase totals = $1,063.80       $1,144.3341   $1,144.33   $1,144.35   $1,144.40