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 $189.75   10.679%   $210.0134   $210.01   $210.00   $210.00  
  Purchase #2 $127.84   13.149%   $144.6497   $144.65   $144.65   $144.60  
  Purchase #3 $163.90   6.238%   $174.1241   $174.12   $174.10   $174.10  
  Purchase #4 $84.59   7.360%   $90.8158   $90.82   $90.80   $90.80  
  Purchase #5 $23.81   12.140%   $26.7005   $26.70   $26.70   $26.70  
  Purchase #6 $212.91   7.613%   $229.1188   $229.12   $229.10   $229.10  
  Purchase #7 $195.99   4.192%   $204.2059   $204.21   $204.20   $204.20  
  7 purchase totals = $998.79       $1,079.6282   $1,079.63   $1,079.55   $1,079.50