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 $63.43   5.639%   $67.0068   $67.01   $67.00   $67.00  
  Purchase #2 $23.59   6.520%   $25.1281   $25.13   $25.15   $25.10  
  Purchase #3 $115.87   3.186%   $119.5616   $119.56   $119.55   $119.60  
  Purchase #4 $111.37   5.246%   $117.2125   $117.21   $117.20   $117.20  
  Purchase #5 $120.25   5.478%   $126.8373   $126.84   $126.85   $126.80  
  Purchase #6 $191.51   6.533%   $204.0213   $204.02   $204.00   $204.00  
  Purchase #7 $217.78   3.569%   $225.5526   $225.55   $225.55   $225.60  
  7 purchase totals = $843.80       $885.3202   $885.32   $885.30   $885.30