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 $76.61   13.783%   $87.1692   $87.17   $87.15   $87.20  
  Purchase #2 $135.77   12.107%   $152.2077   $152.21   $152.20   $152.20  
  Purchase #3 $250.57   3.137%   $258.4304   $258.43   $258.45   $258.40  
  Purchase #4 $118.68   10.163%   $130.7414   $130.74   $130.75   $130.70  
  Purchase #5 $126.59   9.303%   $138.3667   $138.37   $138.35   $138.40  
  Purchase #6 $117.82   7.437%   $126.5823   $126.58   $126.60   $126.60  
  Purchase #7 $148.55   9.865%   $163.2045   $163.20   $163.20   $163.20  
  7 purchase totals = $974.59       $1,056.7022   $1,056.70   $1,056.70   $1,056.70