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 $199.87   9.774%   $219.4053   $219.41   $219.40   $219.40  
  Purchase #2 $207.96   9.761%   $228.259   $228.26   $228.25   $228.30  
  Purchase #3 $178.54   4.196%   $186.0315   $186.03   $186.05   $186.00  
  Purchase #4 $159.72   7.817%   $172.2053   $172.21   $172.20   $172.20  
  Purchase #5 $91.54   6.356%   $97.3583   $97.36   $97.35   $97.40  
  Purchase #6 $197.57   9.647%   $216.6296   $216.63   $216.65   $216.60  
  Purchase #7 $149.66   9.800%   $164.3267   $164.33   $164.35   $164.30  
  7 purchase totals = $1,184.86       $1,284.2157   $1,284.23   $1,284.25   $1,284.20