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 $156.96   12.587%   $176.7166   $176.72   $176.70   $176.70  
  Purchase #2 $228.29   7.410%   $245.2063   $245.21   $245.20   $245.20  
  Purchase #3 $126.80   7.112%   $135.818   $135.82   $135.80   $135.80  
  Purchase #4 $200.30   3.656%   $207.623   $207.62   $207.60   $207.60  
  Purchase #5 $9.56   11.118%   $10.6229   $10.62   $10.60   $10.60  
  Purchase #6 $95.70   12.334%   $107.5036   $107.50   $107.50   $107.50  
  Purchase #7 $247.43   10.763%   $274.0609   $274.06   $274.05   $274.10  
  7 purchase totals = $1,065.04       $1,157.5513   $1,157.55   $1,157.45   $1,157.50