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 $184.36   5.216%   $193.9762   $193.98   $194.00   $194.00  
  Purchase #2 $46.30   7.282%   $49.6716   $49.67   $49.65   $49.70  
  Purchase #3 $124.46   7.809%   $134.1791   $134.18   $134.20   $134.20  
  Purchase #4 $88.64   3.685%   $91.9064   $91.91   $91.90   $91.90  
  Purchase #5 $70.64   5.825%   $74.7548   $74.75   $74.75   $74.80  
  Purchase #6 $227.46   8.411%   $246.5917   $246.59   $246.60   $246.60  
  Purchase #7 $63.78   9.761%   $70.0056   $70.01   $70.00   $70.00  
  7 purchase totals = $805.64       $861.0854   $861.09   $861.10   $861.20