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 $84.94   9.813%   $93.2752   $93.28   $93.30   $93.30  
  Purchase #2 $218.92   7.592%   $235.5404   $235.54   $235.55   $235.50  
  Purchase #3 $246.27   12.559%   $277.199   $277.20   $277.20   $277.20  
  Purchase #4 $79.68   11.266%   $88.6567   $88.66   $88.65   $88.70  
  Purchase #5 $243.68   12.583%   $274.3423   $274.34   $274.35   $274.30  
  Purchase #6 $28.26   6.300%   $30.0404   $30.04   $30.05   $30.00  
  Purchase #7 $90.93   9.363%   $99.4438   $99.44   $99.45   $99.40  
  7 purchase totals = $992.68       $1,098.4978   $1,098.50   $1,098.55   $1,098.40