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 $58.33   12.634%   $65.6994   $65.70   $65.70   $65.70  
  Purchase #2 $225.58   9.830%   $247.7545   $247.75   $247.75   $247.80  
  Purchase #3 $239.72   7.548%   $257.8141   $257.81   $257.80   $257.80  
  Purchase #4 $179.58   4.160%   $187.0505   $187.05   $187.05   $187.10  
  Purchase #5 $25.56   12.769%   $28.8238   $28.82   $28.80   $28.80  
  Purchase #6 $127.75   8.197%   $138.2217   $138.22   $138.20   $138.20  
  Purchase #7 $126.53   5.545%   $133.5461   $133.55   $133.55   $133.50  
  7 purchase totals = $983.05       $1,058.9101   $1,058.90   $1,058.85   $1,058.90