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 $250.91   13.855%   $285.6736   $285.67   $285.65   $285.70  
  Purchase #2 $57.34   4.274%   $59.7907   $59.79   $59.80   $59.80  
  Purchase #3 $80.89   3.788%   $83.9541   $83.95   $83.95   $84.00  
  Purchase #4 $233.65   12.667%   $263.2464   $263.25   $263.25   $263.20  
  Purchase #5 $106.99   3.189%   $110.4019   $110.40   $110.40   $110.40  
  Purchase #6 $243.94   5.594%   $257.586   $257.59   $257.60   $257.60  
  Purchase #7 $194.91   3.122%   $200.9951   $201.00   $201.00   $201.00  
  7 purchase totals = $1,168.63       $1,261.6478   $1,261.65   $1,261.65   $1,261.70