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 $158.96   10.739%   $176.0307   $176.03   $176.05   $176.00  
  Purchase #2 $229.84   9.492%   $251.6564   $251.66   $251.65   $251.70  
  Purchase #3 $85.60   10.716%   $94.7729   $94.77   $94.75   $94.80  
  Purchase #4 $148.63   5.484%   $156.7809   $156.78   $156.80   $156.80  
  Purchase #5 $130.31   6.565%   $138.8649   $138.86   $138.85   $138.90  
  Purchase #6 $199.67   6.349%   $212.347   $212.35   $212.35   $212.30  
  Purchase #7 $202.94   9.694%   $222.613   $222.61   $222.60   $222.60  
  7 purchase totals = $1,155.95       $1,253.0658   $1,253.06   $1,253.05   $1,253.10