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 $83.88   9.752%   $92.06   $92.06   $92.05   $92.10  
  Purchase #2 $186.42   9.368%   $203.8838   $203.88   $203.90   $203.90  
  Purchase #3 $181.32   4.290%   $189.0986   $189.10   $189.10   $189.10  
  Purchase #4 $148.67   4.213%   $154.9335   $154.93   $154.95   $154.90  
  Purchase #5 $194.56   13.407%   $220.6447   $220.64   $220.65   $220.60  
  Purchase #6 $168.37   10.297%   $185.7071   $185.71   $185.70   $185.70  
  Purchase #7 $131.45   6.561%   $140.0744   $140.07   $140.05   $140.10  
  7 purchase totals = $1,094.67       $1,186.4021   $1,186.39   $1,186.40   $1,186.40