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 $176.49   11.108%   $196.0945   $196.09   $196.10   $196.10  
  Purchase #2 $45.46   9.793%   $49.9119   $49.91   $49.90   $49.90  
  Purchase #3 $216.84   9.317%   $237.043   $237.04   $237.05   $237.00  
  Purchase #4 $51.97   4.269%   $54.1886   $54.19   $54.20   $54.20  
  Purchase #5 $246.40   12.728%   $277.7618   $277.76   $277.75   $277.80  
  Purchase #6 $40.98   6.296%   $43.5601   $43.56   $43.55   $43.60  
  Purchase #7 $180.49   12.461%   $202.9809   $202.98   $203.00   $203.00  
  7 purchase totals = $958.63       $1,061.5408   $1,061.53   $1,061.55   $1,061.60