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 $135.75   11.871%   $151.8649   $151.86   $151.85   $151.90  
  Purchase #2 $244.69   9.392%   $267.6713   $267.67   $267.65   $267.70  
  Purchase #3 $63.41   11.424%   $70.654   $70.65   $70.65   $70.70  
  Purchase #4 $242.69   11.867%   $271.49   $271.49   $271.50   $271.50  
  Purchase #5 $85.54   9.558%   $93.7159   $93.72   $93.70   $93.70  
  Purchase #6 $217.31   3.270%   $224.416   $224.42   $224.40   $224.40  
  Purchase #7 $216.31   12.276%   $242.8642   $242.86   $242.85   $242.90  
  7 purchase totals = $1,205.70       $1,322.6763   $1,322.67   $1,322.60   $1,322.80