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 $184.93   5.437%   $194.9846   $194.98   $195.00   $195.00  
  Purchase #2 $160.50   13.142%   $181.5929   $181.59   $181.60   $181.60  
  Purchase #3 $49.78   12.505%   $56.005   $56.01   $56.00   $56.00  
  Purchase #4 $115.53   10.685%   $127.8744   $127.87   $127.85   $127.90  
  Purchase #5 $117.79   9.473%   $128.9482   $128.95   $128.95   $128.90  
  Purchase #6 $84.50   4.826%   $88.578   $88.58   $88.60   $88.60  
  Purchase #7 $58.60   3.571%   $60.6926   $60.69   $60.70   $60.70  
  7 purchase totals = $771.63       $838.6757   $838.67   $838.70   $838.70