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 $187.33   6.751%   $199.9766   $199.98   $200.00   $200.00  
  Purchase #2 $167.49   6.810%   $178.8961   $178.90   $178.90   $178.90  
  Purchase #3 $50.30   7.734%   $54.1902   $54.19   $54.20   $54.20  
  Purchase #4 $168.28   6.871%   $179.8425   $179.84   $179.85   $179.80  
  Purchase #5 $75.93   11.227%   $84.4547   $84.45   $84.45   $84.50  
  Purchase #6 $199.31   7.273%   $213.8058   $213.81   $213.80   $213.80  
  Purchase #7 $45.61   9.134%   $49.776   $49.78   $49.80   $49.80  
  7 purchase totals = $894.25       $960.9419   $960.95   $961.00   $961.00