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   10.687%   $78.953   $78.95   $78.95   $79.00  
  Purchase #2 $58.74   12.259%   $65.9409   $65.94   $65.95   $65.90  
  Purchase #3 $202.68   12.745%   $228.5116   $228.51   $228.50   $228.50  
  Purchase #4 $157.61   10.459%   $174.0944   $174.09   $174.10   $174.10  
  Purchase #5 $184.65   13.634%   $209.8252   $209.83   $209.85   $209.80  
  Purchase #6 $203.64   13.127%   $230.3718   $230.37   $230.35   $230.40  
  Purchase #7 $23.64   3.821%   $24.5433   $24.54   $24.55   $24.50  
  7 purchase totals = $902.29       $1,012.2402   $1,012.23   $1,012.25   $1,012.20