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 $58.48   4.723%   $61.242   $61.24   $61.25   $61.20  
  Purchase #2 $171.37   5.626%   $181.0113   $181.01   $181.00   $181.00  
  Purchase #3 $45.82   5.246%   $48.2237   $48.22   $48.20   $48.20  
  Purchase #4 $188.72   8.679%   $205.099   $205.10   $205.10   $205.10  
  Purchase #5 $120.51   10.629%   $133.319   $133.32   $133.30   $133.30  
  Purchase #6 $159.48   9.512%   $174.6497   $174.65   $174.65   $174.60  
  Purchase #7 $202.46   7.596%   $217.8389   $217.84   $217.85   $217.80  
  7 purchase totals = $946.84       $1,021.3836   $1,021.38   $1,021.35   $1,021.20