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 $87.36   10.717%   $96.7224   $96.72   $96.70   $96.70  
  Purchase #2 $61.29   4.654%   $64.1424   $64.14   $64.15   $64.10  
  Purchase #3 $206.44   4.428%   $215.5812   $215.58   $215.60   $215.60  
  Purchase #4 $209.32   12.108%   $234.6645   $234.66   $234.65   $234.70  
  Purchase #5 $170.96   5.568%   $180.4791   $180.48   $180.50   $180.50  
  Purchase #6 $109.26   3.270%   $112.8328   $112.83   $112.85   $112.80  
  Purchase #7 $150.28   5.295%   $158.2373   $158.24   $158.25   $158.20  
  7 purchase totals = $994.91       $1,062.6597   $1,062.65   $1,062.70   $1,062.60