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 $177.34   8.785%   $192.9193   $192.92   $192.90   $192.90  
  Purchase #2 $31.30   11.162%   $34.7937   $34.79   $34.80   $34.80  
  Purchase #3 $209.48   9.718%   $229.8373   $229.84   $229.85   $229.80  
  Purchase #4 $112.72   3.427%   $116.5829   $116.58   $116.60   $116.60  
  Purchase #5 $167.35   4.202%   $174.382   $174.38   $174.40   $174.40  
  Purchase #6 $239.27   11.869%   $267.669   $267.67   $267.65   $267.70  
  Purchase #7 $53.80   8.304%   $58.2676   $58.27   $58.25   $58.30  
  7 purchase totals = $991.26       $1,074.4518   $1,074.45   $1,074.45   $1,074.50