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 $91.96   11.213%   $102.2715   $102.27   $102.25   $102.30  
  Purchase #2 $211.57   6.861%   $226.0858   $226.09   $226.10   $226.10  
  Purchase #3 $81.77   5.275%   $86.0834   $86.08   $86.10   $86.10  
  Purchase #4 $216.37   13.326%   $245.2035   $245.20   $245.20   $245.20  
  Purchase #5 $116.30   12.215%   $130.506   $130.51   $130.50   $130.50  
  Purchase #6 $7.84   9.533%   $8.5874   $8.59   $8.60   $8.60  
  Purchase #7 $101.45   11.490%   $113.1066   $113.11   $113.10   $113.10  
  7 purchase totals = $827.26       $911.8442   $911.85   $911.85   $911.90