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 $51.52   10.433%   $56.8951   $56.90   $56.90   $56.90  
  Purchase #2 $198.94   6.270%   $211.4135   $211.41   $211.40   $211.40  
  Purchase #3 $201.63   9.850%   $221.4906   $221.49   $221.50   $221.50  
  Purchase #4 $46.54   5.659%   $49.1737   $49.17   $49.15   $49.20  
  Purchase #5 $192.80   10.518%   $213.0787   $213.08   $213.10   $213.10  
  Purchase #6 $189.94   8.250%   $205.6101   $205.61   $205.60   $205.60  
  Purchase #7 $60.75   8.288%   $65.785   $65.79   $65.80   $65.80  
  7 purchase totals = $942.12       $1,023.4467   $1,023.45   $1,023.45   $1,023.50