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 $145.53   6.531%   $155.0346   $155.03   $155.05   $155.00  
  Purchase #2 $55.60   5.583%   $58.7041   $58.70   $58.70   $58.70  
  Purchase #3 $187.46   5.223%   $197.251   $197.25   $197.25   $197.30  
  Purchase #4 $113.26   9.748%   $124.3006   $124.30   $124.30   $124.30  
  Purchase #5 $43.34   3.869%   $45.0168   $45.02   $45.00   $45.00  
  Purchase #6 $174.77   11.239%   $194.4124   $194.41   $194.40   $194.40  
  Purchase #7 $234.87   10.415%   $259.3317   $259.33   $259.35   $259.30  
  7 purchase totals = $954.83       $1,034.0512   $1,034.04   $1,034.05   $1,034.00