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 $9.62   12.572%   $10.8294   $10.83   $10.85   $10.80  
  Purchase #2 $184.84   5.246%   $194.5367   $194.54   $194.55   $194.50  
  Purchase #3 $208.30   5.467%   $219.6878   $219.69   $219.70   $219.70  
  Purchase #4 $55.96   5.179%   $58.8582   $58.86   $58.85   $58.90  
  Purchase #5 $91.69   11.304%   $102.0546   $102.05   $102.05   $102.10  
  Purchase #6 $141.91   13.457%   $161.0068   $161.01   $161.00   $161.00  
  Purchase #7 $6.96   12.754%   $7.8477   $7.85   $7.85   $7.80  
  7 purchase totals = $699.28       $754.8212   $754.83   $754.85   $754.80