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 $174.65   6.718%   $186.383   $186.38   $186.40   $186.40  
  Purchase #2 $119.74   7.190%   $128.3493   $128.35   $128.35   $128.30  
  Purchase #3 $156.96   13.772%   $178.5765   $178.58   $178.60   $178.60  
  Purchase #4 $130.58   9.282%   $142.7004   $142.70   $142.70   $142.70  
  Purchase #5 $153.32   13.734%   $174.377   $174.38   $174.40   $174.40  
  Purchase #6 $129.41   12.736%   $145.8917   $145.89   $145.90   $145.90  
  Purchase #7 $10.26   13.678%   $11.6634   $11.66   $11.65   $11.70  
  7 purchase totals = $874.92       $967.9413   $967.94   $968.00   $968.00