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 $237.57   11.207%   $264.1945   $264.19   $264.20   $264.20  
  Purchase #2 $156.92   4.218%   $163.5389   $163.54   $163.55   $163.50  
  Purchase #3 $98.97   12.595%   $111.4353   $111.44   $111.45   $111.40  
  Purchase #4 $80.44   9.323%   $87.9394   $87.94   $87.95   $87.90  
  Purchase #5 $43.98   13.493%   $49.9142   $49.91   $49.90   $49.90  
  Purchase #6 $95.41   7.488%   $102.5543   $102.55   $102.55   $102.60  
  Purchase #7 $219.90   9.544%   $240.8873   $240.89   $240.90   $240.90  
  7 purchase totals = $933.19       $1,020.4639   $1,020.46   $1,020.50   $1,020.40