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 $205.28   3.266%   $211.9844   $211.98   $212.00   $212.00  
  Purchase #2 $91.92   5.328%   $96.8175   $96.82   $96.80   $96.80  
  Purchase #3 $88.67   7.772%   $95.5614   $95.56   $95.55   $95.60  
  Purchase #4 $211.82   10.588%   $234.2475   $234.25   $234.25   $234.20  
  Purchase #5 $181.77   10.258%   $200.416   $200.42   $200.40   $200.40  
  Purchase #6 $248.66   11.518%   $277.3007   $277.30   $277.30   $277.30  
  Purchase #7 $79.90   9.761%   $87.699   $87.70   $87.70   $87.70  
  7 purchase totals = $1,108.02       $1,204.0265   $1,204.03   $1,204.00   $1,204.00