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 $169.77   8.144%   $183.5961   $183.60   $183.60   $183.60  
  Purchase #2 $52.96   10.779%   $58.6686   $58.67   $58.65   $58.70  
  Purchase #3 $102.99   7.213%   $110.4187   $110.42   $110.40   $110.40  
  Purchase #4 $183.96   10.852%   $203.9233   $203.92   $203.90   $203.90  
  Purchase #5 $23.27   7.311%   $24.9713   $24.97   $24.95   $25.00  
  Purchase #6 $144.38   8.611%   $156.8126   $156.81   $156.80   $156.80  
  Purchase #7 $214.95   4.164%   $223.9005   $223.90   $223.90   $223.90  
  7 purchase totals = $892.28       $962.2911   $962.29   $962.20   $962.30