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 $53.34   12.871%   $60.2054   $60.21   $60.20   $60.20  
  Purchase #2 $220.56   9.217%   $240.889   $240.89   $240.90   $240.90  
  Purchase #3 $194.76   4.190%   $202.9204   $202.92   $202.90   $202.90  
  Purchase #4 $184.28   7.723%   $198.5119   $198.51   $198.50   $198.50  
  Purchase #5 $83.85   5.102%   $88.128   $88.13   $88.15   $88.10  
  Purchase #6 $180.79   10.356%   $199.5126   $199.51   $199.50   $199.50  
  Purchase #7 $56.27   4.268%   $58.6716   $58.67   $58.65   $58.70  
  7 purchase totals = $973.85       $1,048.8389   $1,048.84   $1,048.80   $1,048.80