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 $57.67   10.664%   $63.8199   $63.82   $63.80   $63.80  
  Purchase #2 $149.39   12.326%   $167.8038   $167.80   $167.80   $167.80  
  Purchase #3 $142.29   6.430%   $151.4392   $151.44   $151.45   $151.40  
  Purchase #4 $247.93   10.401%   $273.7172   $273.72   $273.70   $273.70  
  Purchase #5 $221.78   13.618%   $251.982   $251.98   $252.00   $252.00  
  Purchase #6 $64.50   8.807%   $70.1805   $70.18   $70.20   $70.20  
  Purchase #7 $55.58   6.445%   $59.1621   $59.16   $59.15   $59.20  
  7 purchase totals = $939.14       $1,038.1047   $1,038.10   $1,038.10   $1,038.10