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 $187.38   8.742%   $203.7608   $203.76   $203.75   $203.80  
  Purchase #2 $191.81   6.861%   $204.9701   $204.97   $204.95   $205.00  
  Purchase #3 $48.91   13.413%   $55.4703   $55.47   $55.45   $55.50  
  Purchase #4 $136.53   9.530%   $149.5413   $149.54   $149.55   $149.50  
  Purchase #5 $122.91   7.201%   $131.7607   $131.76   $131.75   $131.80  
  Purchase #6 $43.47   9.347%   $47.5331   $47.53   $47.55   $47.50  
  Purchase #7 $23.55   7.235%   $25.2538   $25.25   $25.25   $25.30  
  7 purchase totals = $754.56       $818.2901   $818.28   $818.25   $818.40