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 $80.90   7.728%   $87.152   $87.15   $87.15   $87.20  
  Purchase #2 $77.58   12.222%   $87.0618   $87.06   $87.05   $87.10  
  Purchase #3 $7.91   10.557%   $8.7451   $8.75   $8.75   $8.70  
  Purchase #4 $180.25   11.382%   $200.7661   $200.77   $200.75   $200.80  
  Purchase #5 $221.43   3.432%   $229.0295   $229.03   $229.05   $229.00  
  Purchase #6 $173.30   7.657%   $186.5696   $186.57   $186.55   $186.60  
  Purchase #7 $230.60   11.338%   $256.7454   $256.75   $256.75   $256.70  
  7 purchase totals = $971.97       $1,056.0695   $1,056.08   $1,056.05   $1,056.10