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 $71.33   5.761%   $75.4393   $75.44   $75.45   $75.40  
  Purchase #2 $118.31   9.633%   $129.7068   $129.71   $129.70   $129.70  
  Purchase #3 $52.47   11.308%   $58.4033   $58.40   $58.40   $58.40  
  Purchase #4 $177.73   6.715%   $189.6646   $189.66   $189.65   $189.70  
  Purchase #5 $66.79   7.281%   $71.653   $71.65   $71.65   $71.70  
  Purchase #6 $183.59   10.771%   $203.3645   $203.36   $203.35   $203.40  
  Purchase #7 $21.30   12.625%   $23.9891   $23.99   $24.00   $24.00  
  7 purchase totals = $691.52       $752.2206   $752.21   $752.20   $752.30