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 $167.29   8.496%   $181.503   $181.50   $181.50   $181.50  
  Purchase #2 $228.96   9.513%   $250.741   $250.74   $250.75   $250.70  
  Purchase #3 $142.34   4.682%   $149.0044   $149.00   $149.00   $149.00  
  Purchase #4 $232.47   7.778%   $250.5515   $250.55   $250.55   $250.60  
  Purchase #5 $228.91   11.425%   $255.063   $255.06   $255.05   $255.10  
  Purchase #6 $179.64   7.764%   $193.5872   $193.59   $193.60   $193.60  
  Purchase #7 $130.84   10.479%   $144.5507   $144.55   $144.55   $144.60  
  7 purchase totals = $1,310.45       $1,425.0008   $1,424.99   $1,425.00   $1,425.10