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 $211.51   12.365%   $237.6632   $237.66   $237.65   $237.70  
  Purchase #2 $24.72   3.835%   $25.668   $25.67   $25.65   $25.70  
  Purchase #3 $250.72   7.469%   $269.4463   $269.45   $269.45   $269.40  
  Purchase #4 $202.86   3.227%   $209.4063   $209.41   $209.40   $209.40  
  Purchase #5 $161.50   10.785%   $178.9178   $178.92   $178.90   $178.90  
  Purchase #6 $27.59   4.541%   $28.8429   $28.84   $28.85   $28.80  
  Purchase #7 $52.42   11.705%   $58.5558   $58.56   $58.55   $58.60  
  7 purchase totals = $931.32       $1,008.5003   $1,008.51   $1,008.45   $1,008.50