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 $54.80   6.446%   $58.3324   $58.33   $58.35   $58.30  
  Purchase #2 $222.82   4.466%   $232.7711   $232.77   $232.75   $232.80  
  Purchase #3 $71.27   12.673%   $80.302   $80.30   $80.30   $80.30  
  Purchase #4 $203.30   4.293%   $212.0277   $212.03   $212.05   $212.00  
  Purchase #5 $147.57   12.592%   $166.152   $166.15   $166.15   $166.20  
  Purchase #6 $246.98   12.487%   $277.8204   $277.82   $277.80   $277.80  
  Purchase #7 $72.53   12.381%   $81.5099   $81.51   $81.50   $81.50  
  7 purchase totals = $1,019.27       $1,108.9155   $1,108.91   $1,108.90   $1,108.90