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 $232.62   6.487%   $247.7101   $247.71   $247.70   $247.70  
  Purchase #2 $108.66   10.701%   $120.2877   $120.29   $120.30   $120.30  
  Purchase #3 $165.80   3.489%   $171.5848   $171.58   $171.60   $171.60  
  Purchase #4 $180.66   3.392%   $186.788   $186.79   $186.80   $186.80  
  Purchase #5 $131.70   6.355%   $140.0695   $140.07   $140.05   $140.10  
  Purchase #6 $74.34   5.369%   $78.3313   $78.33   $78.35   $78.30  
  Purchase #7 $198.37   3.484%   $205.2812   $205.28   $205.30   $205.30  
  7 purchase totals = $1,092.15       $1,150.0526   $1,150.05   $1,150.10   $1,150.10