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 $243.38   6.733%   $259.7668   $259.77   $259.75   $259.80  
  Purchase #2 $128.92   4.560%   $134.7988   $134.80   $134.80   $134.80  
  Purchase #3 $66.42   11.846%   $74.2881   $74.29   $74.30   $74.30  
  Purchase #4 $19.75   13.651%   $22.4461   $22.45   $22.45   $22.40  
  Purchase #5 $163.29   3.168%   $168.463   $168.46   $168.45   $168.50  
  Purchase #6 $45.87   10.278%   $50.5845   $50.58   $50.60   $50.60  
  Purchase #7 $39.35   13.263%   $44.569   $44.57   $44.55   $44.60  
  7 purchase totals = $706.98       $754.9163   $754.92   $754.90   $755.00