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 $129.50   3.507%   $134.0416   $134.04   $134.05   $134.00  
  Purchase #2 $142.55   5.807%   $150.8279   $150.83   $150.85   $150.80  
  Purchase #3 $59.74   7.623%   $64.294   $64.29   $64.30   $64.30  
  Purchase #4 $111.29   5.182%   $117.057   $117.06   $117.05   $117.10  
  Purchase #5 $67.81   3.777%   $70.3712   $70.37   $70.35   $70.40  
  Purchase #6 $211.97   6.474%   $225.6929   $225.69   $225.70   $225.70  
  Purchase #7 $223.82   10.676%   $247.715   $247.72   $247.70   $247.70  
  7 purchase totals = $946.68       $1,009.9996   $1,010.00   $1,010.00   $1,010.00