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 $67.49   3.805%   $70.058   $70.06   $70.05   $70.10  
  Purchase #2 $54.51   11.570%   $60.8168   $60.82   $60.80   $60.80  
  Purchase #3 $139.42   7.110%   $149.3328   $149.33   $149.35   $149.30  
  Purchase #4 $215.31   3.708%   $223.2937   $223.29   $223.30   $223.30  
  Purchase #5 $147.51   13.669%   $167.6731   $167.67   $167.65   $167.70  
  Purchase #6 $194.82   4.474%   $203.5362   $203.54   $203.55   $203.50  
  Purchase #7 $163.91   7.513%   $176.2246   $176.22   $176.20   $176.20  
  7 purchase totals = $982.97       $1,050.9352   $1,050.93   $1,050.90   $1,050.90