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 $216.67   6.425%   $230.591   $230.59   $230.60   $230.60  
  Purchase #2 $235.75   7.568%   $253.5916   $253.59   $253.60   $253.60  
  Purchase #3 $148.70   11.609%   $165.9626   $165.96   $165.95   $166.00  
  Purchase #4 $17.91   10.575%   $19.804   $19.80   $19.80   $19.80  
  Purchase #5 $29.34   5.668%   $31.003   $31.00   $31.00   $31.00  
  Purchase #6 $115.86   5.632%   $122.3852   $122.39   $122.40   $122.40  
  Purchase #7 $120.91   5.274%   $127.2868   $127.29   $127.30   $127.30  
  7 purchase totals = $885.14       $950.6242   $950.62   $950.65   $950.70