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 $103.68   7.569%   $111.5275   $111.53   $111.55   $111.50  
  Purchase #2 $177.31   13.663%   $201.5359   $201.54   $201.55   $201.50  
  Purchase #3 $141.35   13.291%   $160.1368   $160.14   $160.15   $160.10  
  Purchase #4 $29.54   12.552%   $33.2479   $33.25   $33.25   $33.20  
  Purchase #5 $56.74   9.363%   $62.0526   $62.05   $62.05   $62.10  
  Purchase #6 $88.85   9.170%   $96.9975   $97.00   $97.00   $97.00  
  Purchase #7 $80.28   6.741%   $85.6917   $85.69   $85.70   $85.70  
  7 purchase totals = $677.75       $751.1899   $751.20   $751.25   $751.10