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 $97.87   7.152%   $104.8697   $104.87   $104.85   $104.90  
  Purchase #2 $93.93   11.439%   $104.6747   $104.67   $104.65   $104.70  
  Purchase #3 $195.45   3.355%   $202.0073   $202.01   $202.00   $202.00  
  Purchase #4 $246.69   3.553%   $255.4549   $255.45   $255.45   $255.50  
  Purchase #5 $44.45   3.332%   $45.9311   $45.93   $45.95   $45.90  
  Purchase #6 $221.52   8.655%   $240.6926   $240.69   $240.70   $240.70  
  Purchase #7 $64.30   9.798%   $70.6001   $70.60   $70.60   $70.60  
  7 purchase totals = $964.21       $1,024.2304   $1,024.22   $1,024.20   $1,024.30