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 $70.37   5.128%   $73.9786   $73.98   $74.00   $74.00  
  Purchase #2 $230.89   11.736%   $257.9873   $257.99   $258.00   $258.00  
  Purchase #3 $165.27   11.667%   $184.5521   $184.55   $184.55   $184.60  
  Purchase #4 $52.29   6.458%   $55.6669   $55.67   $55.65   $55.70  
  Purchase #5 $48.96   9.781%   $53.7488   $53.75   $53.75   $53.70  
  Purchase #6 $221.68   12.847%   $250.1592   $250.16   $250.15   $250.20  
  Purchase #7 $80.27   7.400%   $86.21   $86.21   $86.20   $86.20  
  7 purchase totals = $869.73       $962.3029   $962.31   $962.30   $962.40