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 $92.55   5.683%   $97.8096   $97.81   $97.80   $97.80  
  Purchase #2 $100.49   5.855%   $106.3737   $106.37   $106.35   $106.40  
  Purchase #3 $65.90   9.146%   $71.9272   $71.93   $71.95   $71.90  
  Purchase #4 $70.65   7.311%   $75.8152   $75.82   $75.80   $75.80  
  Purchase #5 $203.47   6.356%   $216.4026   $216.40   $216.40   $216.40  
  Purchase #6 $243.97   8.842%   $265.5418   $265.54   $265.55   $265.50  
  Purchase #7 $85.34   7.776%   $91.976   $91.98   $92.00   $92.00  
  7 purchase totals = $862.37       $925.8461   $925.85   $925.85   $925.80