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 $24.27   6.472%   $25.8408   $25.84   $25.85   $25.80  
  Purchase #2 $242.26   9.419%   $265.0785   $265.08   $265.10   $265.10  
  Purchase #3 $95.75   7.356%   $102.7934   $102.79   $102.80   $102.80  
  Purchase #4 $5.56   10.307%   $6.1331   $6.13   $6.15   $6.10  
  Purchase #5 $31.74   4.306%   $33.1067   $33.11   $33.10   $33.10  
  Purchase #6 $47.64   12.631%   $53.6574   $53.66   $53.65   $53.70  
  Purchase #7 $18.53   11.297%   $20.6233   $20.62   $20.60   $20.60  
  7 purchase totals = $465.75       $507.2332   $507.23   $507.25   $507.20