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 $239.50   11.467%   $266.9635   $266.96   $266.95   $267.00  
  Purchase #2 $98.29   5.454%   $103.6507   $103.65   $103.65   $103.70  
  Purchase #3 $9.49   7.707%   $10.2214   $10.22   $10.20   $10.20  
  Purchase #4 $135.31   7.374%   $145.2878   $145.29   $145.30   $145.30  
  Purchase #5 $25.84   6.479%   $27.5142   $27.51   $27.50   $27.50  
  Purchase #6 $136.55   13.873%   $155.4936   $155.49   $155.50   $155.50  
  Purchase #7 $38.30   7.837%   $41.3016   $41.30   $41.30   $41.30  
  7 purchase totals = $683.28       $750.4328   $750.42   $750.40   $750.50