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 $95.83   11.273%   $106.6329   $106.63   $106.65   $106.60  
  Purchase #2 $169.42   7.820%   $182.6686   $182.67   $182.65   $182.70  
  Purchase #3 $229.75   7.423%   $246.8043   $246.80   $246.80   $246.80  
  Purchase #4 $157.93   8.717%   $171.6968   $171.70   $171.70   $171.70  
  Purchase #5 $245.93   6.552%   $262.0433   $262.04   $262.05   $262.00  
  Purchase #6 $139.49   9.369%   $152.5588   $152.56   $152.55   $152.60  
  Purchase #7 $120.94   11.164%   $134.4417   $134.44   $134.45   $134.40  
  7 purchase totals = $1,159.29       $1,256.8464   $1,256.84   $1,256.85   $1,256.80