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 $233.35   10.112%   $256.9464   $256.95   $256.95   $256.90  
  Purchase #2 $16.54   6.367%   $17.5931   $17.59   $17.60   $17.60  
  Purchase #3 $194.64   4.694%   $203.7764   $203.78   $203.80   $203.80  
  Purchase #4 $156.82   5.723%   $165.7948   $165.79   $165.80   $165.80  
  Purchase #5 $127.25   8.323%   $137.841   $137.84   $137.85   $137.80  
  Purchase #6 $211.53   4.450%   $220.9431   $220.94   $220.95   $220.90  
  Purchase #7 $38.60   7.479%   $41.4869   $41.49   $41.50   $41.50  
  7 purchase totals = $978.73       $1,044.3817   $1,044.38   $1,044.45   $1,044.30