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 $119.30   10.406%   $131.7144   $131.71   $131.70   $131.70  
  Purchase #2 $151.48   12.125%   $169.847   $169.85   $169.85   $169.80  
  Purchase #3 $14.57   3.235%   $15.0413   $15.04   $15.05   $15.00  
  Purchase #4 $230.95   12.568%   $259.9758   $259.98   $260.00   $260.00  
  Purchase #5 $168.42   3.727%   $174.697   $174.70   $174.70   $174.70  
  Purchase #6 $86.51   8.134%   $93.5467   $93.55   $93.55   $93.50  
  Purchase #7 $210.47   10.553%   $232.6809   $232.68   $232.70   $232.70  
  7 purchase totals = $981.70       $1,077.5031   $1,077.51   $1,077.55   $1,077.40