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 $192.73   5.182%   $202.7173   $202.72   $202.70   $202.70  
  Purchase #2 $207.92   10.191%   $229.1091   $229.11   $229.10   $229.10  
  Purchase #3 $34.69   4.834%   $36.3669   $36.37   $36.35   $36.40  
  Purchase #4 $238.93   12.384%   $268.5191   $268.52   $268.50   $268.50  
  Purchase #5 $227.49   5.767%   $240.6093   $240.61   $240.60   $240.60  
  Purchase #6 $149.41   9.209%   $163.1692   $163.17   $163.15   $163.20  
  Purchase #7 $63.32   8.711%   $68.8358   $68.84   $68.85   $68.80  
  7 purchase totals = $1,114.49       $1,209.3267   $1,209.34   $1,209.25   $1,209.30