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 $63.80   11.279%   $70.996   $71.00   $71.00   $71.00  
  Purchase #2 $117.59   8.320%   $127.3735   $127.37   $127.35   $127.40  
  Purchase #3 $122.36   12.751%   $137.9621   $137.96   $137.95   $138.00  
  Purchase #4 $79.37   10.603%   $87.7856   $87.79   $87.80   $87.80  
  Purchase #5 $44.98   6.786%   $48.0323   $48.03   $48.05   $48.00  
  Purchase #6 $32.31   5.323%   $34.0299   $34.03   $34.05   $34.00  
  Purchase #7 $221.77   11.142%   $246.4796   $246.48   $246.50   $246.50  
  7 purchase totals = $682.18       $752.6590   $752.66   $752.70   $752.70