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 $177.43   8.154%   $191.8976   $191.90   $191.90   $191.90  
  Purchase #2 $230.33   8.614%   $250.1706   $250.17   $250.15   $250.20  
  Purchase #3 $43.54   6.785%   $46.4942   $46.49   $46.50   $46.50  
  Purchase #4 $56.73   6.121%   $60.2024   $60.20   $60.20   $60.20  
  Purchase #5 $168.32   7.761%   $181.3833   $181.38   $181.40   $181.40  
  Purchase #6 $246.90   7.673%   $265.8446   $265.84   $265.85   $265.80  
  Purchase #7 $25.79   3.108%   $26.5916   $26.59   $26.60   $26.60  
  7 purchase totals = $949.04       $1,022.5843   $1,022.57   $1,022.60   $1,022.60