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 $176.34   5.348%   $185.7707   $185.77   $185.75   $185.80  
  Purchase #2 $230.67   3.361%   $238.4228   $238.42   $238.40   $238.40  
  Purchase #3 $193.97   5.492%   $204.6228   $204.62   $204.60   $204.60  
  Purchase #4 $145.29   13.732%   $165.2412   $165.24   $165.25   $165.20  
  Purchase #5 $131.65   13.191%   $149.016   $149.02   $149.00   $149.00  
  Purchase #6 $247.57   7.526%   $266.2021   $266.20   $266.20   $266.20  
  Purchase #7 $26.39   6.457%   $28.094   $28.09   $28.10   $28.10  
  7 purchase totals = $1,151.88       $1,237.3696   $1,237.36   $1,237.30   $1,237.30