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 $154.41   7.121%   $165.4055   $165.41   $165.40   $165.40  
  Purchase #2 $234.30   4.153%   $244.0305   $244.03   $244.05   $244.00  
  Purchase #3 $59.54   9.765%   $65.3541   $65.35   $65.35   $65.40  
  Purchase #4 $225.96   11.183%   $251.2291   $251.23   $251.25   $251.20  
  Purchase #5 $82.40   6.258%   $87.5566   $87.56   $87.55   $87.60  
  Purchase #6 $159.96   5.588%   $168.8986   $168.90   $168.90   $168.90  
  Purchase #7 $68.67   7.183%   $73.6026   $73.60   $73.60   $73.60  
  7 purchase totals = $985.24       $1,056.0770   $1,056.08   $1,056.10   $1,056.10