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 $147.93   13.341%   $167.6653   $167.67   $167.65   $167.70  
  Purchase #2 $105.35   11.465%   $117.4284   $117.43   $117.45   $117.40  
  Purchase #3 $120.95   9.317%   $132.2189   $132.22   $132.20   $132.20  
  Purchase #4 $235.53   13.280%   $266.8084   $266.81   $266.80   $266.80  
  Purchase #5 $195.37   12.230%   $219.2638   $219.26   $219.25   $219.30  
  Purchase #6 $49.41   13.677%   $56.1678   $56.17   $56.15   $56.20  
  Purchase #7 $129.36   5.464%   $136.4282   $136.43   $136.45   $136.40  
  7 purchase totals = $983.90       $1,095.9808   $1,095.99   $1,095.95   $1,096.00