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 $65.96   11.340%   $73.4399   $73.44   $73.45   $73.40  
  Purchase #2 $203.50   3.109%   $209.8268   $209.83   $209.85   $209.80  
  Purchase #3 $118.65   7.864%   $127.9806   $127.98   $128.00   $128.00  
  Purchase #4 $70.84   3.761%   $73.5043   $73.50   $73.50   $73.50  
  Purchase #5 $48.72   11.841%   $54.4889   $54.49   $54.50   $54.50  
  Purchase #6 $11.65   4.655%   $12.1923   $12.19   $12.20   $12.20  
  Purchase #7 $77.87   4.699%   $81.5291   $81.53   $81.55   $81.50  
  7 purchase totals = $597.19       $632.9619   $632.96   $633.05   $632.90