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 $53.96   8.698%   $58.6534   $58.65   $58.65   $58.70  
  Purchase #2 $117.26   5.779%   $124.0365   $124.04   $124.05   $124.00  
  Purchase #3 $68.31   6.833%   $72.9776   $72.98   $73.00   $73.00  
  Purchase #4 $202.40   4.421%   $211.3481   $211.35   $211.35   $211.30  
  Purchase #5 $6.34   10.651%   $7.0153   $7.02   $7.00   $7.00  
  Purchase #6 $91.44   5.795%   $96.7389   $96.74   $96.75   $96.70  
  Purchase #7 $127.85   11.508%   $142.563   $142.56   $142.55   $142.60  
  7 purchase totals = $667.56       $713.3328   $713.34   $713.35   $713.30