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 $191.57   10.373%   $211.4416   $211.44   $211.45   $211.40  
  Purchase #2 $147.60   10.323%   $162.8367   $162.84   $162.85   $162.80  
  Purchase #3 $150.51   5.580%   $158.9085   $158.91   $158.90   $158.90  
  Purchase #4 $183.82   8.620%   $199.6653   $199.67   $199.65   $199.70  
  Purchase #5 $71.68   3.155%   $73.9415   $73.94   $73.95   $73.90  
  Purchase #6 $185.71   6.597%   $197.9613   $197.96   $197.95   $198.00  
  Purchase #7 $24.81   12.717%   $27.9651   $27.97   $27.95   $28.00  
  7 purchase totals = $955.70       $1,032.7200   $1,032.73   $1,032.70   $1,032.70