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 $169.48   11.605%   $189.1482   $189.15   $189.15   $189.10  
  Purchase #2 $247.67   12.189%   $277.8585   $277.86   $277.85   $277.90  
  Purchase #3 $49.95   7.322%   $53.6073   $53.61   $53.60   $53.60  
  Purchase #4 $25.37   4.849%   $26.6002   $26.60   $26.60   $26.60  
  Purchase #5 $148.31   6.771%   $158.3521   $158.35   $158.35   $158.40  
  Purchase #6 $16.49   4.338%   $17.2053   $17.21   $17.20   $17.20  
  Purchase #7 $243.84   11.331%   $271.4695   $271.47   $271.45   $271.50  
  7 purchase totals = $901.11       $994.2411   $994.25   $994.20   $994.30