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 $110.59   10.341%   $122.0261   $122.03   $122.05   $122.00  
  Purchase #2 $167.53   12.816%   $189.0006   $189.00   $189.00   $189.00  
  Purchase #3 $108.91   10.205%   $120.0243   $120.02   $120.00   $120.00  
  Purchase #4 $249.53   10.670%   $276.1549   $276.15   $276.15   $276.20  
  Purchase #5 $50.93   8.847%   $55.4358   $55.44   $55.45   $55.40  
  Purchase #6 $145.59   4.754%   $152.5113   $152.51   $152.50   $152.50  
  Purchase #7 $106.29   3.163%   $109.652   $109.65   $109.65   $109.70  
  7 purchase totals = $939.37       $1,024.8050   $1,024.80   $1,024.80   $1,024.80