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 $63.48   3.212%   $65.519   $65.52   $65.50   $65.50  
  Purchase #2 $16.69   11.336%   $18.582   $18.58   $18.60   $18.60  
  Purchase #3 $217.32   8.332%   $235.4271   $235.43   $235.45   $235.40  
  Purchase #4 $128.42   11.864%   $143.6557   $143.66   $143.65   $143.70  
  Purchase #5 $68.44   13.346%   $77.574   $77.57   $77.55   $77.60  
  Purchase #6 $127.55   10.707%   $141.2068   $141.21   $141.20   $141.20  
  Purchase #7 $160.70   6.368%   $170.9334   $170.93   $170.95   $170.90  
  7 purchase totals = $782.60       $852.8980   $852.90   $852.90   $852.90