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 $84.57   13.814%   $96.2525   $96.25   $96.25   $96.30  
  Purchase #2 $118.39   5.232%   $124.5842   $124.58   $124.60   $124.60  
  Purchase #3 $86.31   12.612%   $97.1954   $97.20   $97.20   $97.20  
  Purchase #4 $19.40   13.701%   $22.058   $22.06   $22.05   $22.10  
  Purchase #5 $113.25   6.363%   $120.4561   $120.46   $120.45   $120.50  
  Purchase #6 $206.67   8.479%   $224.1935   $224.19   $224.20   $224.20  
  Purchase #7 $172.34   9.257%   $188.2935   $188.29   $188.30   $188.30  
  7 purchase totals = $800.93       $873.0332   $873.03   $873.05   $873.20