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 $144.87   13.112%   $163.8654   $163.87   $163.85   $163.90  
  Purchase #2 $150.65   12.325%   $169.2176   $169.22   $169.20   $169.20  
  Purchase #3 $81.97   4.502%   $85.6603   $85.66   $85.65   $85.70  
  Purchase #4 $172.64   3.871%   $179.3229   $179.32   $179.30   $179.30  
  Purchase #5 $52.38   8.478%   $56.8208   $56.82   $56.80   $56.80  
  Purchase #6 $204.64   7.290%   $219.5583   $219.56   $219.55   $219.60  
  Purchase #7 $194.60   13.257%   $220.3981   $220.40   $220.40   $220.40  
  7 purchase totals = $1,001.75       $1,094.8434   $1,094.85   $1,094.75   $1,094.90