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 $195.39   3.627%   $202.4768   $202.48   $202.50   $202.50  
  Purchase #2 $204.65   3.837%   $212.5024   $212.50   $212.50   $212.50  
  Purchase #3 $91.80   12.789%   $103.5403   $103.54   $103.55   $103.50  
  Purchase #4 $90.51   6.770%   $96.6375   $96.64   $96.65   $96.60  
  Purchase #5 $130.34   11.856%   $145.7931   $145.79   $145.80   $145.80  
  Purchase #6 $236.95   12.720%   $267.09   $267.09   $267.10   $267.10  
  Purchase #7 $110.43   11.556%   $123.1913   $123.19   $123.20   $123.20  
  7 purchase totals = $1,060.07       $1,151.2314   $1,151.23   $1,151.30   $1,151.20