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 $83.87   11.147%   $93.219   $93.22   $93.20   $93.20  
  Purchase #2 $240.97   11.456%   $268.5755   $268.58   $268.60   $268.60  
  Purchase #3 $250.36   4.696%   $262.1169   $262.12   $262.10   $262.10  
  Purchase #4 $103.43   5.572%   $109.1931   $109.19   $109.20   $109.20  
  Purchase #5 $14.96   11.665%   $16.7051   $16.71   $16.70   $16.70  
  Purchase #6 $104.79   10.558%   $115.8537   $115.85   $115.85   $115.90  
  Purchase #7 $76.37   5.180%   $80.326   $80.33   $80.35   $80.30  
  7 purchase totals = $874.75       $945.9893   $946.00   $946.00   $946.00