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 $146.71   3.245%   $151.4707   $151.47   $151.45   $151.50  
  Purchase #2 $194.55   4.178%   $202.6783   $202.68   $202.70   $202.70  
  Purchase #3 $179.58   11.829%   $200.8225   $200.82   $200.80   $200.80  
  Purchase #4 $46.42   7.615%   $49.9549   $49.95   $49.95   $50.00  
  Purchase #5 $145.52   4.111%   $151.5023   $151.50   $151.50   $151.50  
  Purchase #6 $186.44   13.506%   $211.6206   $211.62   $211.60   $211.60  
  Purchase #7 $27.72   9.219%   $30.2755   $30.28   $30.30   $30.30  
  7 purchase totals = $926.94       $998.3248   $998.32   $998.30   $998.40