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 $118.58   12.752%   $133.7013   $133.70   $133.70   $133.70  
  Purchase #2 $209.98   8.219%   $227.2383   $227.24   $227.25   $227.20  
  Purchase #3 $187.96   8.317%   $203.5926   $203.59   $203.60   $203.60  
  Purchase #4 $130.75   3.467%   $135.2831   $135.28   $135.30   $135.30  
  Purchase #5 $88.58   4.868%   $92.8921   $92.89   $92.90   $92.90  
  Purchase #6 $195.51   8.217%   $211.5751   $211.58   $211.60   $211.60  
  Purchase #7 $6.76   9.438%   $7.398   $7.40   $7.40   $7.40  
  7 purchase totals = $938.12       $1,011.6805   $1,011.68   $1,011.75   $1,011.70