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 $56.91   5.470%   $60.023   $60.02   $60.00   $60.00  
  Purchase #2 $194.78   7.190%   $208.7847   $208.78   $208.80   $208.80  
  Purchase #3 $119.68   6.135%   $127.0224   $127.02   $127.00   $127.00  
  Purchase #4 $120.54   6.280%   $128.1099   $128.11   $128.10   $128.10  
  Purchase #5 $90.73   9.687%   $99.519   $99.52   $99.50   $99.50  
  Purchase #6 $60.84   7.761%   $65.5618   $65.56   $65.55   $65.60  
  Purchase #7 $66.99   10.538%   $74.0494   $74.05   $74.05   $74.00  
  7 purchase totals = $710.47       $763.0702   $763.06   $763.00   $763.00